Practical guides, roundups, and explainers on the tools and concepts that show up in day-to-day work — all written for use alongside the free tools on the rest of the site.
193 posts.
A practical guide to counting: the difference between permutations (order matters) and combinations (order does not), the formula for each, the common real-world cases, and how to run the calculation in your browser without pulling out a calculator or a textbook.
A practical guide to splitting equity between co-founders: the four factors that actually drive a fair split, the standard 4-year vesting with 1-year cliff, why equal splits are usually wrong, and how to use a simple calculator to test your split before it is too late to change.
JSON files get long fast. A 5,000-line config file or a 50 KB API response is unreadable as raw text. This guide covers the right way to navigate a JSON document: tree views, search, path navigation, and the moves that turn a wall of text into something you can actually work with.
Color contrast is the most-measured accessibility metric on the web. This guide explains the WCAG 2.2 contrast formula, the AA and AAA thresholds, and how to make sure your site is usable for people with low vision.
A sitemap.xml file tells search engines which pages on your site exist. Learn what to include, what to leave out, how to write one by hand or generate one, and how to submit it to Google and Bing.
Your IP address is a public identifier that any website you visit can see. Learn what it exposes (city, ISP, ASN, sometimes a VPN), what it does not expose, and how to check yours without uploading anything.
A practical guide to password-based encryption: how AES-GCM with PBKDF2 actually works, why the wire format matters for future compatibility, the common foot-guns (weak passwords, no integrity check, ECB mode), and how to encrypt a message in your browser without trusting a remote service with the plaintext.
A practical guide to EXIF metadata: what is in it, what it reveals about you, the difference between EXIF and IPTC and XMP, the common cases where you want to strip it, and how to read it in your browser without uploading the photo anywhere.
A practical guide to loan math: the formula, what amortization actually means, the difference between APR and APY, what extra payments really save, and how to get a full amortization schedule in your browser without sending your numbers to a bank.
Stopwatches, countdown timers, and interval clocks are daily tools for cooking, fitness, studying, and meetings. This guide covers when to use which, the right tool, and how to build one yourself in JavaScript.
The exact keyboard shortcuts, gesture, and tools for capturing a screenshot on every major platform. Includes scrolling screenshots, region captures, and how to annotate or extract text from a screenshot.
CIDR notation (the /24 in 192.168.1.0/24) is the standard way to write IP network ranges. Learn what the slash means, how to read any CIDR block, and the practical rules for IPv4 and IPv6.
A practical guide to random numbers: the difference between Math.random and crypto.getRandomValues, why fairness matters for giveaways and raffles, how to roll dice and shuffle a list in your browser, and the one case where randomness is genuinely hard.
A practical guide to BMI: the formula, the four standard categories, why the number is rough, what to use alongside it, and how to calculate it in your browser without sending your data anywhere.
A practical guide to making a professional invoice as a freelancer or small business. What to include, the common mistakes, the right format, and a free browser-based tool that generates a clean PDF without signup, watermarks, or sending your client data to a third party.
A full-page screenshot captures the entire scrollable area of a page, not just the visible viewport. This guide covers the right tool for every browser, every device, and the edge cases (sticky headers, lazy-loaded content, infinite scroll).
A Unix timestamp is the number of seconds (or milliseconds) since January 1, 1970, UTC. This guide explains why it exists, how it works, and the practical consequences — including the Y2038 problem and the 2038 bug.
A favicon is the small icon that appears in browser tabs, bookmarks, and search results. This guide shows the exact sizes, file formats, and HTML needed to add one to any site — plus a free generator that does it in your browser.
A regular expression is a tiny language for matching patterns in text. It is one of the most useful tools in programming — and one of the most overused. Here is what regex is, the four operators that cover 90% of real-world use, the four signs you should not use regex, and how to test one in your browser before you commit it to production.
A practical guide to subtitle formats: the differences between SRT, WebVTT, and MicroDVD SUB, the format compatibility matrix for common players, the timing-shift and FPS-scaling cases that come up when subtitles drift, and how to convert everything in your browser without uploading your file anywhere.
A practical guide to naming a business: what makes a name good in the first place, the test that catches 80% of bad names, how to find an available .com, and the check you should do before you commit. With a free in-browser name generator for brainstorming.
A URL slug is the part of a web address that identifies a specific page. This guide covers what makes a good slug, what to avoid, and how the Uttir Slug Generator handles the most common edge cases.
A practical tour of Uttir's new AI tools category: text summarization, sentiment analysis, text similarity, audio transcription, and background removal — all running on a small model inside your browser. Nothing leaves your device.
A WHOIS or RDAP record tells you who owns a domain, who runs it, and when it expires. Learn what every field means, how to look up any domain in seconds, and what to do with the information.
A good API request has six parts: method, URL, headers, body, authentication, and a way to handle the response. Most failed requests fail because one of those parts is wrong. Here is a tour of what each part does, the common mistakes, and the order in which to debug a failing request.
A practical guide to the six most common readability formulas: Flesch Reading Ease, Flesch-Kincaid Grade, Gunning Fog, SMOG, Coleman-Liau, and ARI. The differences, the math, the right one for the right audience, and how to run all six in your browser without uploading your draft anywhere.
A practical guide to age math: the difference between calendar years and elapsed time, why "years old" is fuzzier than you think, how to handle leap years and time zones, and how to get an exact result in your browser without uploading your birth date to anyone.
A practical guide to HTML-to-PDF conversion: when to use it, the difference between the browser print path and a real PDF library, the formatting gotchas that trip people up, and how to get a clean PDF in your browser without sending the source to anyone.
Combining multiple images (JPG, PNG, WebP) into a single PDF is a daily task for receipts, scans, photo albums, and document workflows. This guide covers the right way to do it, in your browser, without uploading anything.
A PDF (Portable Document Format) is a file format that preserves the exact appearance of a document across every device and operating system. This guide covers how it works, when to use it, and how to work with PDFs without uploading them to a server.
Comparing two text files is a daily task for developers, writers, and anyone who edits the same document twice. This guide covers the algorithms, the tools, and how to read a diff once you have one.
Trailing commas, unquoted keys, single quotes instead of double, comments in JSON, and NaN as a value — the five mistakes that show up in every JSON file that breaks in production. Learn what they are, why parsers reject them, and how to catch them before they ship.
A practical guide to tipping: the standard rates by country, the math for splitting uneven orders, the difference between pre-tax and post-tax tipping, and how to do the whole thing in your browser without a calculator app or a back-of-the-napkin argument.
A practical guide to currency conversion: the data sources, the common pitfalls (bank vs. mid-market rate, fees, daily drift), and how to get a fast, accurate conversion in your browser without uploading your amounts to anyone.
A practical guide to making a meme in your browser: pick a template, write the top and bottom text, and download a clean image. No watermark, no signup, no upload. The right approach for a quick shareable.
Image resolution is the most common performance lever on a website. Too low and images look bad; too high and pages load slowly. This guide covers the right resolution for every use case, the math, and the format trade-offs.
Merging multiple CSV files is a daily task for data analysts, accountants, and anyone who gets data in pieces. This guide covers the right way to do it, the common pitfalls (mismatched columns, encoding, headers), and the tools.
URLs can only contain a small set of characters. Everything else gets percent-encoded as %XX. Learn which characters are reserved, when to encode, and the practical rules for query strings, paths, and form data.
A practical guide to CSS Grid: when to use it (and when flexbox is the better choice), the six properties that matter, how named lines and areas work, and how to experiment with a live layout in your browser before committing it to a stylesheet.
A practical guide to creating a digital signature: when a real drawn signature is the right pick, when a typed name is fine, and the 60-second test that tells you which you need. With a free in-browser drawing tool that produces a transparent PNG.
A practical guide to making and opening zip archives in your browser. When the in-browser approach is the right pick, when a desktop tool is better, and how to handle a multi-file batch without sending the files to a third-party server.
Need an image under 100 KB, 500 KB, or 2 MB for a form, a CMS, or an email attachment? This guide covers the practical techniques that work: quality-based compression, dimension resizing, and format conversion. Includes a free in-browser tool that does all three with a target size.
A photo is a great source for a color palette — the colors already work together. This guide covers the visual approach, the algorithmic approach, and the right tools for designers and developers.
Calculating the days between two dates, or adding days to a date, looks simple but has edge cases. Learn the rules for days, weeks, months, and years, and how to avoid the month-end and leap-year traps.
Your robots.txt file controls which pages search engines are allowed to crawl. Learn the syntax, the most common patterns, the mistakes that can hide your site from Google, and how to write one in 60 seconds.
APR and APY are not the same. APR ignores compounding; APY includes it. The math, the 5% savings example, and how to compare offers properly.
One mechanical horsepower is 745.7 watts. Here is the history, why car engines still use hp, and how to convert to watts, kilowatts, and BTU/hour.
Rent-vs-buy is decided by 6 numbers: rent, price, mortgage rate, holding period, opportunity cost, and rent inflation. The math, breakeven, and a free calculator.
Amortization is how a fixed payment splits between interest and principal. Early on, most of it is interest. The math, the schedule, and a free calculator.
The MET formula estimates calories burned from body weight, activity, and duration. Here is the math, the limits, and a free calculator for 24 common activities.
Overtime is 1.5× the regular rate after 40 hours per week in the US. California adds daily OT and 2× after 12 hours/day. Here is the math, with a free calculator.
Rental yield is the annual rent as a percentage of the property price. Here is gross vs net yield, the cash-on-cash return, and a free calculator that does the math.
A fathom is 6 feet, used for depth soundings, mining, and timber. Here is the history, the math, and how to convert it to meters, feet, and nautical miles.
A nautical mile is 1,852 meters, equal to one minute of arc on a meridian. How it differs from a statute mile, who uses it, and how to convert it to km.
A knot is one nautical mile per hour. Here is the history, the math, and how to convert knots to mph, m/s, ft/s, and km/h for sailing, aviation, and weather.
A kilowatt-hour is the unit your electric bill measures. Here is what kWh means, how to convert it to watts, joules, and BTU, and how to estimate your own usage.
A curated list of the best free CSS tools: gradient generators, box-shadow builders, flexbox / grid playgrounds, minifiers, and animation builders. All run in your browser.
A curated list of the best free API testing tools: HTTP clients, request builders, response inspectors, and mock servers. All browser-based or self-hosted, all free, no signup required.
A curated list of the best free PDF merge tools. All run in your browser, no upload of your documents, no signup, no daily limit. Plus best practices for merging PDFs the right way.
A curated list of the best free favicon generators that work in your browser. ICO, PNG, SVG, and Apple touch icon formats. All run locally, no upload, no signup.
A curated list of the best free Markdown editors and live previewers that run in your browser. No signup, no upload, no tracking. From quick-look previews to full WYSIWYG-style editing.
A curated list of the best free JSON tools: formatter, validator, diff, tree viewer, minifier, schema validator, and YAML/TOML converter. All run in your browser.
A curated list of the best free password generators that run locally in your browser. Cryptographically random, no upload, no history, no tracking.
A curated list of the best free color tools: pickers, palette generators, contrast checkers, format converters, and image-based color extractors. All run locally, no signup, no upload.
A curated list of the best free QR code generators that work in your browser. No signup, no tracking, no limit. From plain-text QR codes to WiFi and vCard.
A curated list of the best free OCR tools that extract text from images and PDFs. All run locally or are privacy-friendly, all free, no signup, no upload of your documents.
A roundup of the best free online calculators for finance, health, fitness, pregnancy, and everyday math — all of which run in your browser and never send your numbers to a server.
A roundup of the best free online unit converters for length, mass, temperature, volume, speed, pressure, energy, and power — all of which run in your browser and never send your numbers to a server.
A curated list of the best free developer tools that run in your browser. Format, validate, generate, convert, debug — all without an account, all without sending your code to a server.
A roundup of the best free image compression tools for JPG, PNG, and WebP. All of them run in your browser, so your photos never leave your device. Some let you target a specific file size in KB.
A roundup of the best free PDF tools for merge, split, compress, convert, OCR, sign, and more — all of which run in your browser and never send your documents to a server.
A stack trace is a map of where your code was when it crashed. Most people read it backwards. The actual bug is almost never where you think it is. Here is how to read a stack trace top-to-bottom, the four lines that matter, the seven lines that lie, and how to find the real bug in 30 seconds.
PDFs are the universal document format for sharing, but the universal pain for editing. You can extract the text for free, in your browser, without uploading the file to a server. Here is the workflow for native-text PDFs (most modern ones) and scanned PDFs (older or image-only ones), with no Adobe subscription required.
Blog images need to be the right size, the right format, and the right quality — usually under 200 KB so the page loads fast. Here are nine browser-based tools that handle every step of a blog image workflow: resizing, compressing, converting, cropping, adding alt text, and generating favicons. All free, all without uploading your images.
Passwords have been around for 60 years. The mistakes people make with them have been around almost as long. Here are the seven most common, why each one is still a problem, and the five-minute fix that closes most of them — including the one nobody talks about (your password manager's master password).
The 25-minute pomodoro is a starting point, not a rule. Some people focus better in 50-minute blocks, some in 90. Some need 5-minute breaks, some need 15. Here is how to build a pomodoro schedule that fits your work, your energy, and your task type, and how to track what is working.
A Unix timestamp is the number of seconds since January 1, 1970, UTC. It is the universal time format for computers: small, sortable, timezone-independent, and trivially comparable. Here is what it is, where you will see one, the Year 2038 problem, and how to convert to and from a human-readable date in your browser.
A sitemap is a file that lists every page on your website in a format search engines can read. It is the most basic SEO tool, and most websites either do not have one or have one with errors. Here is what a sitemap does, the format, how to generate one without uploading your site to a server, and the seven things that go wrong.
A CSV is a flat table. JSON is a tree. Converting between them is one of the most common tasks in modern data work, and a good converter handles quoting, escapes, type inference, and the dozen edge cases that bite you in production. Here is what a converter does, and how to convert without uploading your data.
If a tool is free and you are not the customer, you are the product. That is the standard line. It is true for most free online tools. Here is what it actually costs, what we do instead to keep this site free, and the four things you can check in 30 seconds to know if a free tool is selling you.
Most bots announce themselves in the User-Agent string. A few pretend to be real browsers. Here are the seven reliable signals, the order to check them, and how to look up any user agent in a browser-based parser to see exactly what kind of client is hitting your site.
A good invoice has six required fields and one optional one. Most invoice generators bury those fields behind an account wall. Here is what goes in each field, the seven mistakes that make invoices hard to pay, and how to generate one in your browser without uploading your financial data anywhere.
SRT is the most common subtitle format: numbered cues with start and end timestamps and the text to display. Learn the structure, why it has weird line breaks, how to convert SRT to VTT or SUB, and how to fix the three most common mistakes (off-by-one timing, encoding, and Windows line endings).
A 5MB JSON blob with thousands of nested keys is not a file, it is a maze. A tree view lets you collapse what you do not need, search across the whole document, copy a single value, and find the path to a field in seconds. Here is how to use one, and how to keep your document on your device.
You can make HTTP requests, inspect headers, send JSON bodies, and check response status without installing a desktop client. The browser is enough. Here is a practical workflow using only a free, browser-based tool that keeps your requests on your device.
A cron expression is a 5-field syntax for scheduling recurring tasks. Learn what each field means, the special characters (*, /, -, ,), common patterns (every minute, every hour, weekdays at 9am), and how to build one without memorising the syntax.
Math.random() is not secure. Learn why, what "secure" means for random number generation, the right browser API to use (crypto.getRandomValues), and how to generate a random number in a range without bias.
A URL slug is the human-readable part of a URL after the domain. Good slugs are short, descriptive, stable, and lowercase. Learn the rules, the tradeoffs, why "auto-generated IDs" are usually better than pretty slugs, and how to generate one that will not bite you in six months.
A syntactically valid email address is not the same as a deliverable one. Learn the three layers of email validation (syntax, domain, mailbox), what each catches, what each misses, and the right tool for each — without sending a single test message.
Meta tag generators, SERP previewers, keyword density checkers, JSON-LD generators, sitemap builders, and robots.txt writers — seven free SEO tools that cover the on-page work Ahrefs and SEMrush charge $99/month for. No signup, no upload, no account.
Aspect ratio is the proportional relationship between an image's width and height. Learn the standard ratios (4:3, 3:2, 16:9, 1:1), why photographers obsess over them, how to calculate the right crop for a target ratio, and the difference between aspect ratio and resolution.
Minification shrinks your HTML, CSS, and JavaScript files by removing whitespace, comments, and dead code. Learn what it does, what it does not do, when to use it, and how to safely minify a file in your browser without uploading the source.
Color pickers, palette generators, contrast checkers, color name finders, and converters — eight free color tools that run in your browser, do not upload your images or palettes, and cover every color task a designer actually has.
The Pomodoro Technique is a 25-minute focus timer with 5-minute breaks, invented in the late 1980s. It works because of how attention and fatigue actually behave, not because of the timer. Learn the original rules, the science, the variations, and how to run a Pomodoro session in your browser.
Pretty SQL is readable SQL. Learn the formatting rules senior engineers use (uppercase keywords, aligned columns, consistent indentation, no SELECT *), why they matter, and how to format any query automatically in your browser.
Lorem ipsum is placeholder text designers and developers use to fill a layout before the real copy exists. Learn where it came from, when to use it, when not to, and how to generate the right amount of it for your project.
Every photo you take with a smartphone contains EXIF metadata: the camera make and model, the date and time, and — if you have location services on — the GPS coordinates of where you took it. Before sharing a photo publicly, strip the EXIF. Here is the 3-step workflow: check the metadata, remove it, verify the result. The whole thing takes 2 minutes per photo.
Twelve free online tools that are genuinely useful and not on the front page of every "best of" list: a CSS box-shadow generator, a JWT decoder, a binary-to-hex converter, a regex tester with explanations, a Cron expression generator, an EXIF metadata viewer, a CSS gradient maker, a base32 encoder, an HTTP status code reference, a JSON tree viewer, a UUID generator with history, and a CSS clip-path playground. All run in your browser, no signup, no upload.
A 4-step workflow to convert a CSV file to JSON in your browser: paste the CSV, pick the delimiter, pick the conversion mode (array of objects, array of arrays, or keyed object), copy the JSON. The whole thing takes 30 seconds, runs entirely in the browser, and never sends your data to a server. Works for any CSV up to a few MB.
A CSV is a plain text file where each row is a line and each column is separated by a comma. That is the whole spec. Despite being that simple, CSV is the universal interchange format for tabular data: every spreadsheet, database, CRM, analytics tool, and accounting app can import and export it. Here is why it has lasted 50 years and what to watch for.
Plain text is 60 years old and still the most durable, portable, searchable, scriptable, and future-proof format for human-written information. Every note-taking app eventually becomes a plain-text export or a dead format. Plain text files in a folder, indexed by grep, are a tool that will outlive every app you use today. Here is the case.
A spreadsheet is overkill for one-off calculations: a tip, a BMI, a percentage change, a loan payment, a tip split, an age, and a unit conversion. The free calculator tools on this site do each of these in 5 seconds, run in your browser, and never ask you to log in or upload anything. Here is when to use which.
A 5-step workflow to extract a working color palette from any logo image: pick the dominant color, generate 4 supporting colors using a 60-30-10 rule, check contrast for accessibility, test the palette in dark mode, and export the hex codes. Takes 5 minutes once you have done it twice.
A JWT is three base64 strings joined by dots. The middle one is the payload, and it is usually readable without any verification. The header tells you the algorithm. The signature is what you would verify to trust the contents. Here is how to read each part, with worked examples.
Phishing URLs are designed to look real at a glance. The 6 things to look for in the domain (lookalike characters, extra subdomains, wrong TLD, mismatched display vs. actual URL, suspicious path, and URL-encoded junk) take 10 seconds to scan. Here is the checklist, with worked examples.
A cron expression is 5 fields, each a number, a wildcard, or a step. Once you know what each field means and how the steps work, the expressions stop looking like a typo and start looking like a tiny schedule. Here is the cheat sheet, in plain language.
The favicon started as a single 16×16 ICO file in 1999. In 2026, a complete favicon setup is 8 files: a 16×16, 32×32, 180×180 (Apple), 192×192, 512×512 (PWA), a manifest.json, and a site.webmanifest. Here is the 27-year history and what you actually need today.
A free tier is a marketing budget, not a price. The vendor is paying for your signup, your usage, and your data, expecting a conversion later. The conversion usually comes at the moment when switching is hardest. Here are 6 cases where the paid tier is the cheaper choice.
UUIDs look like a free win for primary keys: globally unique, no coordination, no information leak. The reality is more nuanced. They are 2x larger, 2-5x slower to index, and split awkwardly in B-tree indexes. Here is the honest tradeoff.
A good email signature has 4-6 lines: name, role, company, contact, and a single link. A bad one has a logo, a quote, three social icons, a disclaimer, and a phone number in tiny gray text. Here is what to include, what to cut, and seven examples.
There are six image formats that matter in 2026: PNG, JPG, WebP, AVIF, HEIC, and SVG. Each has a specific use case. Using the wrong one costs you 3-10x in file size, in quality, or in compatibility. Here is the honest field guide.
Most temperature converter APIs use a single formula: T(F) = T(C) × 9/5 + 32. The formula is correct. The implementation is usually wrong. Here is why, when it matters, and how to verify.
There is a point in every debugging session, every refactor, every "let me just check this real quick" where the right tool is no tool. The mouse goes down. The terminal closes. The thinking begins. Here is when to step away from the tool, when not to, and the cost of getting it wrong.
A stopwatch counts up. A countdown counts down. They look like the same tool with the direction flipped. They are not. The physics of measuring time, the cognitive load of waiting, and the use cases are different. Here is why.
A "secure" password is no longer the bottleneck. The bottleneck is everything around the password. Here is what the threat model actually looks like in 2026, why a 16-character random password is not enough on its own, and the four things that actually keep you safe.
A pretentious color palette is one that tries too hard. It uses 12 colors when 4 would do, picks unique hues for every button, or insists on "sophisticated" muted tones that look the same on screen. Here are the five signs, why each one is a problem, and what to do instead.
Words per minute is the most common typing speed metric, but it is not what you think. Here is what WPM actually counts, why 5-characters-per-word is the convention, what "net WPM" vs "gross WPM" means, why your accuracy matters more than your speed past a certain point, and how to actually get faster.
A decision maker is a tiebreaker, not a replacement for judgment. Here is when it actually helps (analysis-paralysis on equal options, breaking a long deadlock, choosing between two equivalent things), and when it makes things worse (when one option is clearly better, when you have not done the analysis, when the decision matters and you need to own it).
Nine free image tools that work in your browser without uploading your photos to a server. Convert, compress, resize, crop, color-pick, and read EXIF in seconds — no account, no upload, no watermark.
Eight free PDF tools that work in your browser without uploading your files to a server. Merge, split, compress, convert, OCR, sign, and edit PDFs in seconds — no account, no upload, no watermark.
A practical guide to QR codes in 2026: the 8 most useful non-obvious uses (Wi-Fi sharing, contact cards, restaurant menus, payment, event tickets, two-factor backup, package tracking, and table-top donation), the 3 cases where QR codes are a bad idea, and how to generate a working code in your browser without uploading anything.
A practical guide to choosing a color palette: the 5 rules that separate a working palette from a decorative one (60-30-10 distribution, start with one color, neutrals are colors, contrast beats hue, test in context), common mistakes, and how to use a browser-based palette generator without uploading anything.
A practical guide to JSON viewers and formatters: the 8 best browser-based tools in 2026, what makes each one different, the privacy question (most popular JSON viewers upload your data), and how to format, validate, and explore JSON without sending it to a remote server.
A practical guide to JSON Schema: what it is (a way to describe the shape of valid JSON), why it matters (catches bugs at the API boundary, generates docs, powers form libraries), the basic syntax, and how to start using it in your own projects.
A practical guide to content formats: the three choices (Markdown, HTML, rich text), the trade-offs (readability, control, portability), the right format for each use case (blog, documentation, email, code, books), and the conversion workflow that keeps everything in sync.
A practical guide to CSS color naming: the difference between HEX, RGB, HSL, and named colors; why "tomato" looks the way it does; how to find the right name for a color you can see; the most useful CSS named colors by category; and how to find them in your browser without uploading anything.
A practical guide to cryptographic hash functions: what a hash is for, the four real-world choices (MD5, SHA-1, SHA-256, SHA-3), the speed vs. security trade-offs, the deprecation timeline, and which one to use for each common use case.
The six password mistakes almost everyone makes in 2026: weak passwords, password reuse, no 2FA, storing in browsers, sharing via text, and ignoring breach notifications. What actually goes wrong, the realistic cost of each, and the five-minute fix for each one.
A color picker tells you the color of a single pixel. But a pixel is not a color — it is a sample of a continuous function, and the sample is usually wrong. Here is why, when it matters, and what to do about it.
Markdown is the universal plain-text format; HTML is the universal markup language. Learn the difference, when you need to convert between them, and how to do it in your browser with no upload, no library, and no build step.
Smallpdf, iLovePDF, Adobe Acrobat, and the in-browser alternatives — how they compare on privacy, quality, file-size limits, and price. Plus a free in-browser PDF merger that never uploads your documents.
TinyPNG, Squoosh, Compressor.io, and the new wave of in-browser image compressors — how they compare on quality, privacy, batch size, and price. Plus a free in-browser image compressor that never uploads your photos.
Postman, Insomnia, Bruno, and the new wave of API clients — compared for features, privacy, and price. Includes a free in-browser API tester for one-off requests.
CSS gradients are images without files. The three types, the syntax that actually matters, how to pick the right color stops, and the patterns that make any gradient look professional.
Base64-encoded images travel as text — useful in CSS, HTML emails, JSON APIs, and anywhere you cannot ship a real image file. The trade-offs, the practical limits, and a free browser tool that does the conversion without uploading anything.
Why a regex like ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-z]{2,}$ is not enough, what to validate server-side vs client-side, and how to catch the typos that lose you real signups.
Turn any logo, photo, or icon into a working favicon — the small image browsers show in tabs, bookmarks, and home-screen shortcuts. Free browser tool, no upload, every size and format you need.
There are 13 meta tags that affect how your page looks in search results, in social shares, and on mobile. Three of them matter for SEO. Five matter for social sharing. The other five are either obsolete or nice-to-have. Here is the cheat sheet, with what each one does and when to skip it.
Three different counts, three different purposes. The formulas, the edge cases that trip people up, and the free tools that do it without uploading your text.
How to read and write Morse code, the full international alphabet chart, common abbreviations, and a free browser-based translator. Plus the surprising places Morse is still used in 2026.
The real reading time formula, why 200 WPM underestimates most readers, the difference between reading and speaking time, and how to use this for content planning.
JSON is forgiving to write and brutal to debug. The five validation mistakes that cause runtime crashes, the right tools to catch them, and a free browser-based validator and formatter.
A decision tree for picking the right image format, when each one wins, and the conversion paths that actually lose no quality. Includes a free browser-based converter.
QR codes aren't just for URLs. The five practical uses that replace typing, the right QR version and error correction for each, and a free browser-based generator.
The percentage change formula, worked examples for prices, grades, salaries, and growth, plus the three mistakes almost everyone makes. Includes a free calculator.
When to convert a PDF to JPG, the right DPI setting for each use case, and how to do it for free without uploading your files. Covers whole documents and single-page extraction.
Combine multiple PDFs into one, in any order, without uploading them to a server. Covers drag-to-reorder, bookmarks, page removal, and common pitfalls.
Learn when JPG, PNG, WebP, and AVIF are the right choice, what quality setting to use, and the exact settings that cut file size by 70–90% with no visible difference.
QR codes are everywhere now, but most people do not know how they work or when to use them over a regular barcode. This guide covers the structure, the error correction, the right size, and the practical design rules.
WCAG contrast ratios depend on lightness, not hue. Learn the math, the AA and AAA thresholds, the “color is not the only signal” rule, and a workflow for testing every pairing before you commit to a palette.
UUID v7 is the 2024 successor to v4 for database primary keys. Learn what changed, why it exists, when to keep v4, and how to migrate without breaking anything.
Apple’s HEIC format saves storage but breaks the moment you try to share a photo. Learn what HEIC is, why it exists, how to convert it to JPG locally without uploading, and the trade-offs of every approach.
Four encodings that all turn binary into text, but with different alphabets, sizes, and URL-safety. This guide explains the differences, the use cases, and the gotchas that trip people up.
Regex looks like noise but it is just a tiny pattern language. This guide teaches the mental model, the most useful metacharacters, the traps, and a workflow for testing patterns without copy-pasting into random websites.
A practical guide to creating passwords that are both uncrackable and memorable: passphrases, password managers, and the one rule that actually matters. Includes a free browser tool to check any password’s strength.
Learn what DNS records are, the most common record types (A, AAAA, MX, TXT, NS, CNAME, SOA, CAA), how to look them up from your browser, and how to use them to verify that a domain points where you think it does.
Standard deviation sounds intimidating but it is just a measure of how spread out your numbers are. Learn what it means, when to use it, and how to calculate it by hand and with a free browser tool.
A practical guide to writing meta descriptions that boost click-through rates, with length rules, examples, and a free browser tool to check yours against Google’s recommended range.
Learn what two-factor authentication really does, how time-based one-time passwords (TOTP) work, why codes change every 30 seconds, and how to inspect your own codes without an authenticator app.
Learn what JWTs are made of, how to decode and verify them, the most common mistakes developers make, and how to inspect a token in your browser without sending it anywhere.
A practical comparison of HEX, RGB, and HSL color formats: when to use each, how to convert between them, and why one of them is the right choice for your next project.
Learn how monthly mortgage payments are calculated, including the formula, an amortization example, and what the numbers mean for your loan. With a free mortgage calculator.
Learn how to resize images for web, email, and social media without losing quality. 5 free methods including the fastest browser-based approach.
A practical guide to Base64 encoding: what it is, how it works, when to use it, and when to use something else. With examples and a free browser-based encoder.
Learn how to shrink a PDF file to 30-70% of its original size without visible quality loss. 5 free methods, including the fastest browser-based approach.
Learn 5 free ways to merge PDF files into a single document, including the fastest browser-based method. No upload, no signup, no watermarks.
A practical comparison of JSON, YAML, and TOML: syntax, features, readability, tooling support, and when each format is the right choice for config files, data exchange, and APIs.
A curated list of the best free online image tools that run in your browser, no upload, no signup. Convert between JPG, PNG, and WebP, compress, resize, crop, and more.
Government forms, job applications, and visa portals all want photos under 100 KB or 200 KB. Here is how to hit those targets without uploading your photo to a server, without losing sharpness, and without paying for Photoshop. A good compressor lets you pick a target size, not a quality slider.
A practical comparison of JPEG, PNG, WebP, AVIF, and SVG: when to use each, how they handle transparency and animation, browser support in 2026, and how to pick the right format for the job.
A complete guide to cron expressions: what each field means, common patterns, special characters (* ? / , -), day-of-week gotchas, and how to test your cron before shipping it.
A practical guide to UUID versions — what v1, v4, v5, and v7 are, how they differ, and why UUID v7 is the right default for new database primary keys in 2026.
Learn what JSON formatting is, why it matters, and how to pretty-print, minify, and validate JSON. Includes common pitfalls, real examples, and a free browser-based JSON formatter.
A curated list of the best free online developer tools that run in your browser, no signup, no uploads, no tracking. Tools for formatting, encoding, testing, and more — the running count is in the body below.
A practical guide to flexbox: when to use it (and when not to), the six properties that matter, the common gotchas with align-items and flex-basis, and how to experiment with a live layout in your browser before committing it to a stylesheet.
A practical guide to barcodes for small business and product teams: the differences between UPC, EAN, Code 128, and QR, when you need a real GS1-issued code, and how to generate a working barcode in your browser in seconds.
A practical guide to keyword density: what it is, what numbers actually matter, the difference between modern keyword analysis and the 2010 stuffing era, and how to run the check in your browser in 10 seconds.
A practical guide to writing headlines that earn both search rankings and click-throughs. The eight dimensions that actually matter, the mistakes that quietly cost you traffic, and a self-check you can run in your browser before publishing.
Markdown is the universal plain-text format for writing on the web. Learn the syntax for every common element, see the rendered output side by side with the source, and bookmark this as a quick reference.
Compound interest is what makes your savings grow and your debt grow faster. Learn the exact formula, how often compounding matters more than the rate, and the spreadsheet layout that lets you model any investment or loan.
Every HTTP status code, what it means, and what to do about it. A practical reference for the codes you actually see in production, with examples for 200, 301, 404, 500, 503, and the obscure ones you have not met yet.
A practical guide to building UTM campaign links that track accurately in Google Analytics: what the five UTM parameters do, the naming conventions that keep your reports clean, and the privacy-first alternatives to the popular SaaS UTM builders that log your campaigns.
A practical guide to writing prose that reads cleanly on the first pass: cut the adverbs, switch to active voice, shorten the long sentences, and know when to ignore every rule. With a self-check you can run in your browser before publishing.
A practical guide to password strength: what makes a password weak, what makes one strong, how password crackers actually work, and how to generate and remember passwords that survive a real attack. Includes a free in-browser password strength checker that never sends your password to a server.
A practical guide to pulling text out of screenshots, scanned documents, photos of signs, and PDFs. What works, what does not, when to use a browser tool, and the accuracy tips that actually matter.
JSON Schema is the standard for describing the structure of JSON data. This guide covers what it is, when to use it, the basic syntax, and how to validate your data in your browser.
Broken URLs hurt SEO, frustrate users, and break the web. This guide covers how to find them (free tools, logs, search console), how to fix them (redirects, rewrites, removals), and how to prevent them in the first place.
A brand color is one color. A color scheme is 5-10 colors that work together. This guide covers how to expand a single brand color into a complete palette using color theory, with practical examples.
A coin flip is the simplest random experiment. The math is 50/50, the physics is messy, and your brain is the worst part. Here is what "fair" actually means, why a flipped coin is not exactly 50/50, why 100 flips rarely show exactly 50/50, and how to verify a tool is using real randomness.
QR codes get mocked as a 2010s relic, but in 2026 they are still the cheapest, fastest, and most universal way to move a phone from a screen to an action. Here is why the alternatives all have a specific failure mode the QR code does not.
A README is the first thing a visitor sees. Most READMEs are walls of text that nobody reads. The good ones are short, scannable, and answer the four questions every visitor has: what is this, why should I care, how do I use it, and how do I install it. Here is the structure, with examples.
Roman numerals look like a relic. They are hard to read, hard to write, and there is no reason to use them in software. Except when there is. Here is the case for keeping them, the cases where they actually help, and the surprising places they still show up.
A good CSS box shadow is subtle, layered, and matches the lighting of the rest of the design. Learn the four-part anatomy of a real shadow (offset, blur, spread, color), the trick of stacking two shadows for depth, and the values that work in production.
