Free Online Developer Tools - Format, Encode & Test in Your Browser
A focused set of free online tools for developers that run entirely in your browser. Format and validate JSON, test regular expressions live, encode and decode Base64, URL, and HTML entities, and pick colors across HEX, RGB, HSL, and OKLCH. No signup, no install, and nothing you paste ever leaves your device.
Gizmoop offers six free online developer tools: a JSON formatter and validator, a color picker, a regex tester, and Base64, URL, and HTML encoders. Each one runs entirely in your browser using client-side JavaScript, so the data you paste is never uploaded or stored. There is no signup, no install, and no usage limit - just open a tool and start working.
All 6 developer tools
Developer utilities that save you from opening Stack Overflow for the fifth time today. Format, validate and minify JSON, encode and decode Base64, URL, and HTML entities, test regular expressions with live match preview and a cheat sheet, and pick colors across HEX, RGB, HSL, and OKLCH formats with Tailwind export and WCAG contrast checks.
Most popular developer
The tools in this category people reach for most often.
All-in-one online developer tools, no signup required
Every developer keeps a handful of small utilities within reach: something to tidy up a JSON response, a way to test a regex before pasting it into code, a quick encoder for a tricky URL. Gizmoop bundles those everyday helpers into one place so you do not have to bookmark six different sites or trust an unfamiliar one with your data.
All six tools are completely free with no usage limit, no account, and no install step. Open the page, paste your input, and get a result. Because each tool is just client-side JavaScript, it works the moment the page finishes loading and keeps working even if your connection drops.
This hub covers a JSON formatter, a color picker, a regex tester, and Base64, URL, and HTML encoders. The sections below explain what each one does and when to reach for it, so you can pick the right tool for the job in seconds.
JSON Formatter - format, validate, and minify JSON online
The JSON Formatter takes a wall of unreadable, single-line JSON and turns it into clean, indented output you can actually scan. Paste an API response or a config blob, click format, and the tool re-indents every nested object and array with consistent spacing and an expandable tree view, so you can drill into deep structures without losing your place.
It also validates as it formats. If a comma is missing, a quote is unbalanced, or a brace never closes, the tool flags the exact problem and points you to the line number rather than failing silently. That makes it ideal for debugging the payloads you get back from a flaky endpoint.
When you are done reading, switch to minify to strip every space and newline back out. Minified JSON is smaller on the wire and in storage, which matters for response sizes, embedded config, and anything you are about to copy into a single-line environment variable.
Color Picker - HEX, RGB, HSL, and OKLCH with a contrast checker
The Color Picker lets you choose a color visually and read it back in whichever format your stylesheet needs. Pick a swatch and instantly see its HEX, RGB, and HSL values, or paste a value you already have to convert it the other way - hex to rgb, rgb to hsl, and back again - without doing the arithmetic by hand.
It also supports OKLCH, the modern perceptual color space that CSS now understands. OKLCH keeps lightness consistent as you shift hue, which makes it far easier to build accessible palettes and smooth gradients than tweaking raw hex values. The tool can export your choices straight to Tailwind format too.
Accessibility is built in. The contrast checker compares a foreground and background color and reports the WCAG contrast ratio, telling you whether the pair passes AA or AAA for normal and large text - so you catch unreadable combinations before they ship instead of after a user complains.
Regex Tester - live regular expression matching with a cheat sheet
Regular expressions are powerful and easy to get subtly wrong, which is exactly why testing them in isolation beats guessing inside your codebase. The Regex Tester gives you a field for your pattern and flags, a field for sample text, and live highlighting that shows every match the instant you type, so you can refine a pattern in tight feedback loops.
It surfaces capture groups separately, so when you are building a replacement or pulling fields out of a string you can confirm each group captures exactly what you expect. Toggling flags like global, case-insensitive, and multiline updates the matches in real time.
A built-in cheat sheet and a library of common patterns sit alongside the editor, so you do not have to remember whether a digit is one syntax or another. It is the fastest way to validate an email or date pattern before committing it to your validation layer.
Base64 Encoder & Decoder - encode binary data as text
Base64 turns arbitrary bytes into a plain-text alphabet that survives systems built for text. The Base64 Encoder converts a string, or even a whole file, into that text form, and the decoder reverses it. This is how you embed a small image as a data URI, drop binary into a JSON field, or carry attachment bytes through email.
Encoding adds roughly a third to the size, so it is a transport convenience rather than a compression trick. It is also worth stressing that Base64 is encoding, not encryption: anyone can decode it back instantly, so never use it to hide passwords, tokens, or other secrets.
Because the tool runs in your browser, you can decode a suspicious-looking Base64 string from a log or a config file without sending it to a third-party server first - a small but real safety improvement when the contents might be sensitive.
URL Encoder & Decoder - percent-encode special characters safely
URLs only allow a limited set of characters, so spaces, ampersands, slashes, and non-ASCII text have to be percent-encoded before they are safe to drop into a query string or path. The URL Encoder does that conversion - a space becomes %20, an ampersand becomes %26 - so your links and request parameters do not break or get truncated.
The decoder goes the other way, turning a percent-encoded string back into readable text. That is handy when you are reading a redirect URL, a logged request, or an OAuth callback and need to see what was actually passed before the encoding obscured it.
Reach for it whenever you are hand-building an API request, constructing a deep link with user-supplied values, or tracking down why a parameter with an ampersand or a plus sign is arriving at the server mangled.
HTML Encoder - escape entities to prevent rendering issues
When text is meant to be shown on a page rather than interpreted as markup, characters like the less-than sign, ampersand, and quotation marks have to be escaped into HTML entities. The HTML Encoder converts them - the less-than sign becomes <, the ampersand becomes & - so the browser displays the literal character instead of trying to parse it as a tag.
This is essential any time you want to show example code or markup inside a page, or display user-generated content without it accidentally injecting elements. Leaving these characters raw is also a classic source of broken layouts and cross-site scripting bugs.
The tool supports named, decimal, and hexadecimal entity forms, and it decodes entities back to plain text too, so you can read content that was escaped somewhere upstream and see exactly what the underlying characters are.
Base64 vs URL vs HTML encoding - which one to use
These three encoders solve different problems and are not interchangeable, so picking the wrong one is a common source of confusion. Base64 makes binary data safe to carry as text. URL encoding makes a string safe to place inside a URL. HTML encoding makes a string safe to display inside a web page without being parsed as markup.
A quick way to decide: if you are moving raw bytes, a file, or an image into a text-only channel, use Base64. If you are putting a value into a query string, a path, or a form-encoded body, use URL encoding. If you are inserting text into HTML that should render as plain characters, use HTML entity encoding.
The encoding quick reference table further down shows the same handful of inputs side by side in all three schemes, which is the fastest way to internalize the difference and confirm you are reaching for the right tool.
100% in-browser and private - your data never leaves your device
Every tool here runs as client-side JavaScript. When you paste JSON, a regex, or a string to encode, that input is processed in your browser and is never uploaded, never logged, and never stored on a server. Close the tab and it is gone.
That matters more than it sounds. The JSON you most want to format is often the JSON you least want to leak - a payload with customer records, an internal API response, an access token in a header. Pasting it into a server-side formatter means trusting an unknown backend with that data. Here, there is no backend to trust, because the work happens entirely on your machine.
It is a genuine privacy and security improvement, not just a marketing line: with nothing transmitted, there is nothing to intercept, retain, or breach.
Why use online dev tools instead of opening an IDE?
For a one-off task, spinning up your editor, finding the right extension or writing a throwaway script is far more work than the task itself. Online dev tools win on setup cost: there is nothing to install, configure, or update, and the tool is ready the instant the page loads.
They are also resource-light and context-free. You can format one ugly response, test one pattern, or decode one string without opening a project, picking an interpreter, or polluting your workspace. That keeps a quick check from derailing whatever you were actually doing.
And they are portable. The same tools work on a locked-down work laptop, a borrowed machine, or a tablet, with no admin rights required - just a modern browser. For deep, repeated work an IDE still wins, but for the small, frequent jobs these tools are simply faster.
Common use cases and who uses these tools
Backend and API developers lean on the JSON formatter to read responses, the Base64 tools to inspect tokens and build data URIs, and the URL encoder to debug request parameters. Front-end developers and designers use the color picker for accessible palettes and contrast, and the HTML encoder to safely display code samples and user content.
Beyond full-time developers, QA engineers test validation patterns with the regex tester, technical writers and students decode strings to understand examples, and anyone wiring up a webhook or a no-code integration ends up needing to encode a value or format a payload.
The common thread is small, frequent, in-the-moment tasks: debugging an API response, fixing a broken link, picking a UI color, or sanity-checking a pattern. These tools exist to make those moments instant.
Encoding quick reference
The same inputs encoded three different ways. Use this to see at a glance how Base64, URL percent-encoding, and HTML entity encoding differ for everyday characters.
| Input | Base64 | URL-encoded | HTML entity |
|---|---|---|---|
| (space) | IA== | %20 | |
| & | Jg== | %26 | & |
| < | PA== | %3C | < |
| " | Ig== | %22 | " |
| Hello World | SGVsbG8gV29ybGQ= | Hello%20World | Hello World |
Frequently asked questions
If you don't find your question here, ask us directly.
Yes. Every developer tool on Gizmoop is completely free with no usage limit, no registration, and no install step. There is no Pro tier and no trial that runs out - the JSON formatter, color picker, regex tester, and the Base64, URL, and HTML encoders are all fully available to everyone, every time.
Yes, here it is. The JSON formatter and every other tool process your input as client-side JavaScript in your browser. Nothing you paste is uploaded, logged, or stored on a server, and it clears the moment you close the tab. That means you can format sensitive payloads without the data ever leaving your device.
No. The tools run entirely in your browser, so there is no network transmission of the data you enter. They keep working even after you go offline because all the processing happens locally. With nothing sent to a server, there is nothing for us to store, log, or expose.
Paste your JSON into the JSON Formatter and click format. The tool re-indents the structure into a readable, expandable tree and validates it at the same time, flagging any syntax error with the exact line number. You can then switch to minify to strip the whitespace back out for a compact, single-line result.
Base64 converts binary data into plain text so it can travel safely through text-only channels - embedding an image as a data URI, putting binary into a JSON field, or sending an email attachment. It adds about a third to the size and is not encryption: anyone can decode it instantly, so never use it to hide secrets.
They follow different rules for different goals. URL (percent) encoding makes characters safe to place inside a URL - a space becomes %20. HTML entity encoding makes text safe to display on a page without being parsed as markup - a less-than sign becomes <. They are not interchangeable; use each for its own context.
Enter your pattern and any flags, then type or paste a test string. The tester highlights every match live as you edit and breaks out capture groups so you can confirm exactly what each one captures. Everything runs in your browser, and a built-in cheat sheet and pattern library help with the syntax.
No. There is nothing to install and no account to create. The tools run in any modern browser - on Windows, Mac, Linux, or mobile - and are ready to use the instant the page loads. Just open the tool you need and start working.
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Gizmoop has 130+ free tools across seven categories.
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Pick a tool above and start formatting, encoding, or testing - free, in your browser, with nothing to install.