DevNestTools — Free Browser-Based Developer Tools

What's here

Each tool does one thing. That's intentional.

The Device Dashboard shows your screen resolution, viewport, pixel ratio, browser, and OS, updating live as you resize. It's useful when someone reports a bug on "their phone" and you need to figure out what phone they're actually talking about. Instead of going back and forth in a Slack thread asking for screenshots and device specs, you send them a link, they open it, and you both see the same information in real time. I built this one originally because I was tired of copy-pasting window.innerWidth calls into the console during QA reviews.

• JSON Beautifier Takes minified or badly formatted JSON and makes it readable. If the JSON is broken, it shows you roughly where the problem is instead of just throwing a generic error. I use this one constantly — not just for APIs, but for cleaning up config files, environment dumps, and clipboard garbage from whatever I was debugging five minutes ago.
• Code Minifier Strips whitespace and comments from HTML, CSS, or JS for quick one-off jobs. You don't always want to fire up Webpack or Vite just to minify a single script. Sometimes you just need a smaller file before a deploy.
• Image Compressor Shrinks JPG, PNG, and WebP files without the quality loss you'd notice. I've used this to cut file sizes in half for blog posts and documentation screenshots. The difference in load time is small for one image, but it adds up when you've got thirty on a page.
• Image to Base64 Converts images into data URIs for embedding in HTML or CSS. Mostly useful for small icons and logos where you want to skip an HTTP request.
• QR Code Generator Makes scannable QR codes from URLs, text, or Wi-Fi credentials. I built this because I needed a QR code for a conference booth sign and couldn't find a free generator that didn't watermark the output or require an account.
• Browser Detector and OS Detector Tells you what browser and OS someone is running. Again, these came out of bug report friction — two people describing the same visual glitch but using different names for the same browser.
• IP Lookup Shows IP and network info for diagnostics. Quick and dirty, nothing fancy.

Why it's built this way

Each tool focuses on one job. That's the whole point.

The JSON Beautifier formats JSON. It doesn't try to validate schemas, compare two files, convert to YAML, or do anything else. Those are all useful features, but they belong in different tools. When you try to make one tool do everything, the interface gets cluttered, the code gets fragile, and the ninety-five percent of people who just want their JSON readable end up lost in options they never asked for.

I've seen tool sites where the "JSON Formatter" page has dropdowns for encoding, indentation depth, schema validation, diffing, and about fifteen other things. Half of them are broken. The other half slow down the page. The actual formatting — the thing you came for — is buried under all of it. That's the opposite of what a tool should do.

Every tool gets tested against real inputs before launch: empty fields, huge files, malformed data, weird edge cases. The JSON Beautifier, for example, has to handle trailing commas (some parsers allow them, some don't), deeply nested structures that would choke a naive implementation, and pasted blobs that are just garbled nonsense from a clipboard copy-paste gone wrong. If something breaks, we'd rather fix the underlying issue than hide it behind a vague error message that tells you nothing useful. You should know what went wrong so you can decide whether to fix your input or report a bug.

New tools show up when they're done. There's no "Coming Soon" section, no placeholder tiles, no fake previews. If it's not built yet, it's just not listed. I'd rather someone leave disappointed that a specific tool doesn't exist yet than land on a preview of something that isn't real and waste their time.

Who uses this

Developers grab these for quick tasks during coding, testing, or debugging. It's the kind of thing you need for about thirty seconds — format some JSON, compress an image, check your viewport — and then you're done. You don't want to install software, create an account, or sit through a loading screen for something that should take less time than reading this sentence.

QA and support teams use the Dashboard and detector tools to get consistent info for bug reports. Instead of "it looks broken on my phone," you get actual device specs that mean something. Two people describing the same issue end up with comparable, useful information instead of two different vague descriptions of "my phone." That alone has probably saved hours of back-and-forth in every team I've worked with.

A lot of non-developers just use the Image Compressor or QR Code Generator because they want something that works fast without signing up. A photographer compressing images before sending them to a client. A teacher making a QR code for a classroom handout. Someone who just needs to shrink a photo enough to attach it to an email. You shouldn't need a CS degree to use a file compressor.

The privacy angle matters too, even if you're not doing anything sensitive. The principle is simple: if you're pasting a JSON payload with API keys in it, or dropping an image with unreleased product shots into a tool, that data shouldn't be leaving your machine. Every tool here runs on your device. You can verify it yourself — open your browser's network tab and watch nothing get sent anywhere. That's not a claim, it's something you can check in ten seconds, and I'd rather you check than take my word for it.

If something's missing

If there's a tool you keep needing and can't find a decent free version of, let us know. A few of these started as exactly that kind of request.

No promises — I'm not going to ship something half-baked just because someone asked — but genuine gaps in what's available tend to stick in my head and eventually turn into new tools when the time is right.