Browser-based tools a developer actually keeps pinned. The bar for this list: the free tier must be genuinely usable, the site must respect its visitors, and it must still work today. Here is what made the cut, in no particular order.
The reference for HTML, CSS, and JavaScript, maintained by Mozilla with the web platform community. When documentation conflicts with reality, MDN is the source that gets corrected first. Its compatibility tables at the bottom of every page end more arguments than any Stack Overflow thread.
Best for: looking up the exact behavior of any web platform API.
Browser support tables for every web feature, with usage-percentage sliders so you can decide whether 92% global support is enough for your audience. The fastest way to answer "can I ship this CSS feature yet?" without reading five blog posts.
Best for: deciding whether a new web feature is safe to use in production.
Google's guidance on building fast, resilient websites: Core Web Vitals explanations, performance patterns, and courses that go deeper than a search result. The measurement tooling (Lighthouse) is documented here alongside the reasoning behind each metric.
Best for: making a slow site fast, with methods that age well.
A full Node.js environment running inside the browser via WebContainers — no servers, no sign-up for quick experiments. Spinning up a React or Vite project takes seconds, which makes it the cleanest way to test a bug report or share a runnable example.
Best for: instant sandboxed projects and shareable bug reproductions.
A virtual whiteboard with a hand-drawn look that makes architecture diagrams approachable instead of intimidating. Nothing to configure: open the page, draw boxes and arrows, export. Scene data stays local unless you choose to share a link.
Best for: architecture sketches and quick diagrams that won't embarrass you in a PR description.
Google's open-source image compressor. Drag an image in, compare codecs (WebP, AVIF, MozJPEG) side by side with a draggable before/after slider, and export — all processing happens locally in your browser. The same philosophy we build with: your files never leave the device.
Best for: squeezing an image to its minimum size without uploading it anywhere.
A shockingly complete Photoshop clone that runs in a browser tab and opens PSD, XCF, and Sketch files natively. The ad-supported free tier has no meaningful feature lock — layers, masks, and filters all work. When you're on a machine without design software, this is the answer.
Best for: editing PSD files on any computer without installing anything.
An infinite canvas drawing tool with unusually good feel — the snapping, smoothing, and selection ergonomics are the benchmark other whiteboards copy. The free web version is generous, and the SDK is open source if you ever want to embed a canvas in your own product.
Best for: freeform brainstorming where precise shapes matter less than speed.
Troy Hunt's breach database: enter an email address and see which known data breaches exposed it. It also offers a password checker that hashes locally (only the first five characters of the SHA-1 hash are sent, never the password itself). If a password you reuse appears here, change it everywhere today.
Best for: checking whether your accounts or passwords are already compromised.
Community-maintained recommendations for private software: browsers, messengers, VPNs, email providers, with the reasoning and trade-offs spelled out rather than just a ranking. It's the reference we point people to when they ask which tools actually respect them.
Best for: choosing privacy-respecting software without wading through marketing.
The Internet Archive's time machine: billions of saved snapshots of the web, going back decades. A deleted documentation page, a redesigned product's old pricing, a source you cited that vanished — if it existed publicly, there's a good chance a snapshot survives here.
Best for: recovering dead pages and checking what a website used to look like.