Every developer has a collection of online tools they use weekly. The problem is most of them are either paywalled, require an account, or quietly upload your files to a server you've never heard of.
This is a list of the best free browser-based tools that require no signup and process everything locally — your data never leaves your device.
I'll be upfront: many of these are from Tooliest, which I built. But I'll also point to alternatives where they genuinely do something better.
JSON tools
What you need: A formatter that handles large files without lagging, validates syntax properly, and ideally shows a tree view.
🔗 Tooliest JSON Formatter — formats, validates, and shows a collapsible tree view. Also has a minifier and a JSON ↔ CSV converter in the same category.
Alternative worth knowing: jsonlint.com — older, simpler, but very fast for quick validation.
PDF tools
What you need: Merge, split, compress, rotate. Most "free" PDF tools online upload your file to their server, show you a download link, and delete it "after 24 hours." Maybe.
🔗 Tooliest PDF Suite — 15 PDF tools, all running via pdf-lib in the browser. The file genuinely never goes anywhere. Covers merge, split, compress, rotate, watermark, password protect, page reorder, extractor, and more.
This is the one category where the no-upload constraint matters most, especially for documents that contain sensitive information.
Regex testing
What you need: Live match highlighting, capture group display, flag toggles, and ideally the ability to test against multiple strings.
🔗 Tooliest Regex Tester — real-time matching with group highlighting as you type.
Alternative: regex101.com — the gold standard for regex testing. More powerful, particularly for complex patterns with full explanation panels. Use regex101 when you need the detailed breakdown; Tooliest when you want it fast in the same tab as your other tools.
Code screenshots
What you need: Syntax-highlighted, shareable code images for Twitter, documentation, or presentations.
🔗 Tooliest Code Screenshot Generator — 20+ themes, 20+ languages, customizable window chrome and gradient backgrounds. Downloads as PNG or SVG. Nothing leaves your browser.
Alternative: ray.so by Raycast — beautiful output, slightly more limited theme options.
CSS generators
Three that actually save time:
🔗 CSS Gradient Generator — linear and radial gradients, live preview, copy-ready CSS output.
🔗 Box Shadow Generator — adjust offset, blur, spread, color, inset. See it live, copy the CSS.
🔗 Flexbox Playground — toggle all flex properties visually. Useful when you forget which direction flex-direction: column goes for the hundredth time.
JWT decoding
What you need: Paste a JWT, see the header and payload decoded, verify the structure.
🔗 Tooliest JWT Decoder — decodes header, payload, and shows the signature section. Entirely client-side — your token never gets sent anywhere, which matters since JWTs often contain auth data.
Alternative: jwt.io — the standard, built by Auth0. More features for signature verification.
Diff checking
What you need: Paste two versions of text or code, see exactly what changed.
🔗 Tooliest Diff Checker — side-by-side comparison with additions and deletions highlighted inline.
Alternative: diffchecker.com — more robust for large files, though the free version now has some limitations.
Image compression
What you need: Drop in a PNG or JPG, get a smaller file without visible quality loss.
🔗 Tooliest Image Compressor — handles JPG, PNG, WebP, AVIF. Canvas-based compression runs locally, nothing uploaded.
Alternative: squoosh.app by Google — the benchmark for browser-based image compression. More codec options, more control. Use Squoosh when quality precision matters; Tooliest when you want fast and frictionless.
Invoice generation
What you need: A professional invoice with your logo, line items, tax calculation, and PDF export — without paying for FreshBooks or Wave.
🔗 Tooliest Invoice Generator — add your logo, line items, tax rates, discounts, and custom notes. Downloads as PDF instantly. Browser-side, no account, works offline.
Cron expression parsing
What you need: You wrote 0 */6 * * 1-5 and now you need to know what that actually runs.
🔗 Tooliest Cron Parser — paste any cron expression, get a plain English description plus next scheduled run times.
Alternative: crontab.guru — the definitive cron tool. More detailed than what I built. Use crontab.guru for cron work specifically.
Chmod calculator
What you need: Convert between symbolic permissions (rwxr-xr--) and octal (754) without doing it in your head at 2 AM.
🔗 Tooliest Chmod Calculator — click the permission checkboxes, get the octal. Or type the octal, get the symbolic. Exactly as simple as it should be.
SQL formatting
What you need: Paste a query that's one long line, get it back indented and readable.
🔗 Tooliest SQL Formatter — keyword highlighting and clean indentation. Handles most standard SQL dialects.
Hash generation
What you need: Generate MD5, SHA-1, SHA-256, or SHA-512 hashes from text or to verify file integrity.
🔗 Tooliest Hash Generator — all four hash types, client-side. Your input never leaves the browser.
Encoding / decoding
Three you'll use constantly:
All browser-side, all instant.
The honest summary
| Use case | Best tool |
|---|---|
| JSON formatting | Tooliest or jsonlint.com |
| PDF merge / split / protect | Tooliest PDF suite — only no-upload option |
| Regex testing | regex101.com for complex patterns |
| Image compression | Squoosh for precision, Tooliest for speed |
| JWT decoding | jwt.io for signature verification |
| Code screenshots | Tooliest or ray.so |
| Cron parsing | crontab.guru |
| Everything else daily | Tooliest — one tab, no switching |
For Regex and JWT work specifically, use the dedicated tools — they go deeper. For everything else in your daily workflow, having one tab that handles it without signup friction is worth more than marginally better features scattered across 12 different sites.
Bookmark this
👉 tooliest.com — 102 tools, one tab, nothing uploaded.
What tools did I miss that you reach for regularly? Drop them in the comments — I'm actively adding to the collection and the best suggestions have always come from other developers.
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