Most "best tools" lists are just affiliate link farms. This one isn't. These are tools that solve real, recurring friction points in day-to-day development — the kind you reach for a dozen times a week without thinking about it. Every tool here runs entirely in your browser, requires no signup, and does exactly what it says on the tin.
The criterion for making this list was simple: if you have to context-switch out of your current task to use it, it needs to be fast, reliable, and free. All ten of these pass that bar.
1 JSON Viewer
Raw JSON from an API response or a config file is nearly unreadable when it comes back as a single flattened string. A good JSON viewer formats it instantly, collapses nodes so you can navigate large objects, and highlights syntax errors before you waste time debugging a malformed payload. EazyStudio's JSON Viewer does all of this client-side — no data leaves your browser.
Use cases: Paste the response body from a REST API call to inspect nested objects without scrolling through a wall of text. Drop in a minified package-lock.json or a config blob to find the key you're looking for in seconds.
Pro tip: If your API is returning a 400 or 500 and the error body looks garbled, paste it into the JSON Viewer first. More often than not it's a JSON parse error that becomes immediately obvious once the structure is visible.
2 JWT Decoder
JWTs are everywhere in modern auth flows, but they're Base64URL-encoded by default, so you can't read them at a glance. The JWT Decoder splits the token into its three parts — header, payload, and signature — and shows you the decoded claims alongside a human-readable expiry time. Everything runs locally; your token never hits a server.
Use cases: Debugging a 401 response? Paste the Authorization header token to check whether it's expired or has the wrong scope claim. Integrating a third-party OAuth provider? Decode the ID token to see exactly what user attributes are being sent.
3 Code Minifier
Before shipping any JavaScript or CSS to production, it should be minified. Smaller files mean faster load times and lower bandwidth costs — which matters especially on mobile connections. The EazyStudio minifier handles JS and CSS, strips comments and whitespace, and gives you a character count before and after so you can see the savings immediately.
Use cases: You've written a small utility script that needs to go into a CMS or an email template where you can't run a build step. Paste it in, minify it, and copy the output. Also useful for shrinking third-party CSS snippets before inlining them into a critical-CSS block.
4 Meta Tags Generator
Writing Open Graph and Twitter Card tags by hand is tedious and error-prone. Miss one attribute and your links look broken when shared on Slack or LinkedIn. The meta tags generator walks you through title, description, image, and canonical URL, then outputs the complete block of tags ready to paste into your <head>.
Use cases: Launching a new landing page and need to get the social preview right before it goes live. Auditing an existing page to see which meta tags are missing. Generating a full OG tag set for a blog post without having to look up the spec again.
5 Base64 Encoder / Decoder
Base64 comes up constantly — encoding binary data for APIs, decoding email attachments, embedding small images as data URIs, reading JWT payloads, or working with Basic Auth headers. Having a fast encoder/decoder in your browser means you don't have to drop into a terminal or remember the exact atob() / btoa() syntax every time.
Use cases: You receive a Basic Auth credential in the format Basic dXNlcjpwYXNz and need to check what username and password it contains. Or you want to encode an SVG as a data URI to inline it into CSS without an extra HTTP request.
6 URL Parser
Long URLs with multiple query parameters are painful to read and debug manually. The URL Parser breaks any URL into its component parts — protocol, hostname, path, and each query parameter as a separate key-value pair — so you can see immediately what's being passed. It also lets you build URLs by adding parameters interactively.
Use cases: Debugging a redirect chain where a URL gets passed through multiple services and accumulated query params. Checking whether a UTM-tagged marketing URL is structured correctly before it goes into a campaign. Reverse-engineering a third-party API URL to understand what parameters are being sent.
7 CSS Beautifier
Minified or auto-generated CSS is unreadable for debugging. The CSS Beautifier takes a compressed stylesheet and re-formats it with proper indentation, line breaks, and consistent spacing. It also works as a linter for obvious syntax issues. Pair it with the minifier — beautify to inspect, minify to ship.
Use cases: You've pulled a vendor stylesheet into your project and need to understand what it's doing before overriding it. A build tool has output a concatenated CSS bundle and you need to trace a specific rule back to its selector without a source map.
8 CSS Grid Generator
CSS Grid is powerful but the mental model for complex layouts takes time to construct. The Grid Generator gives you a visual editor where you define columns and rows, drag to span cells, and get the corresponding CSS output in real time. It removes the back-and-forth between code and browser DevTools when you're prototyping a layout from scratch.
Use cases: Sketching a dashboard layout before you commit to a component structure. Quickly generating the grid boilerplate for a photo gallery or card grid and then customising from there. Teaching yourself CSS Grid by seeing immediately how changes to grid-template-columns affect the visual result.
9 Web Performance Analyzer
Page performance is a shipping requirement, not an afterthought. The Web Performance Analyzer checks Core Web Vitals and key performance metrics for any public URL — load time, resource sizes, render-blocking assets — and gives you actionable findings without having to run a Lighthouse audit locally or wait for a CI pipeline.
Use cases: Quick-checking a client's site before a sales call to identify obvious performance wins. Verifying that a new deployment hasn't introduced a performance regression on a key landing page. Auditing a competitor's site to understand where you have an edge.
10 API Tester
Sometimes you just need to fire an HTTP request quickly — without opening Postman, waiting for it to load, or digging through a saved collection to find the right endpoint. The API Tester handles GET, POST, PUT, DELETE, and PATCH requests, lets you set custom headers and a JSON body, and displays the response with syntax highlighting. It's the "just test this endpoint right now" tool.
Use cases: Confirming that a newly deployed API endpoint is returning the right status code and response shape before wiring it up to the frontend. Testing webhook payloads by sending a POST with a custom JSON body. Checking whether an authentication header is being accepted without having to write a curl command from memory.
All ten tools run entirely in your browser. No account required, no data sent to a server, no usage limits. They're also mobile-friendly — useful when you're debugging something from a phone and can't get to a laptop.
How to Get the Most Out of Browser-Based Dev Tools
The biggest advantage of browser-based tools is zero setup time. There's no install, no version conflict, no "it works on my machine" problem. But to actually make them part of your workflow rather than something you google when you need it, bookmark them. Seriously — a bookmarks folder called "Dev Tools" with these ten links takes thirty seconds to create and will save you time every single week.
A second tip: use them for sanity checks before filing a bug report. Before you open a ticket saying "the API is returning bad data," paste the response into the JSON Viewer and decode the JWT in the auth header. Half the time the problem becomes obvious immediately, and you've saved yourself and a colleague a round-trip of Slack messages.
Finally, these tools are useful for onboarding new developers. Rather than explaining what's inside a JWT or how CSS Grid works abstractly, share a link to the tool and let them interact with real examples. Hands-on beats documentation every time.
Start With the JSON Viewer
The most universally useful tool in the list — format, validate, and explore any JSON payload instantly, right in your browser.
Open JSON Viewer