The utilities you reach for a dozen times a week: pretty-printing and validating JSON, decoding a JWT to see why auth is failing, Base64 and URL encoding, MD5/SHA checksums for text and files, a regex tester with live match highlighting, a line-by-line diff, epoch conversion, CSV to JSON, Markdown preview and WCAG contrast checking.
Every one runs locally with no network call. That's not a marketing line for this category, it's a security requirement: pasting a production JWT, an API response or a customer CSV into a random online formatter is handing that payload to a third party, and those tokens are frequently still valid. You can load these pages, go offline, and keep working.
All developer tools
- JSON Formatter — Pretty-print, minify and validate JSON on the fly.
- Base64 Encode / Decode — Encode and decode Base64 text and files — UTF-8 safe, URL-safe option.
- UUID Generator — Random v4 and time-sortable v7 UUIDs, single or in bulk.
- Hash Generator — MD5, SHA-1, SHA-256 and SHA-512 for text and files.
- Regex Tester — Test regular expressions with live highlighting and groups.
- Diff Checker — Compare two texts line by line — like git diff, in your browser.
- Unix Timestamp Converter — Epoch to date and back — seconds, milliseconds, ISO and local.
- JWT Decoder — Decode JWT headers and payloads locally — with expiry checks.
- CSV to JSON — Convert CSV to JSON and back — quoted fields handled properly.
- URL Encoder / Decoder — Percent-encode or decode text and URLs, with a query-param breakdown.
- Markdown Preview — Live GitHub-flavored Markdown rendering as you type.
- Contrast Checker — WCAG contrast ratios with AA/AAA pass-fail at a glance.
Frequently asked questions
Is it safe to paste a production JWT or API response here?
Yes — the decoder parses the token in your browser with no network request, so nothing is transmitted. It's still worth building the habit of checking: open your devtools network tab while you paste, and confirm nothing goes out. Do that on any online decoder before you trust it with a live token, because plenty do send what you paste.
Do these tools work offline?
Yes, once the page has loaded. There's no server round-trip in any of them, so you can use them on a plane, on a locked-down network, or with the machine disconnected entirely.
Can the hash generator handle large files?
Yes. Hashing uses the Web Crypto API and streams the file, so multi-gigabyte checksums work — the file is read from disk in your browser and never uploaded, which also makes it far faster than any upload-based checksum service.
Does the JWT decoder verify signatures?
It decodes the header and payload and checks the expiry, but does not verify the signature — that would require your signing secret, which should never be pasted into a web page. Use it to inspect claims and debug expiry, not to establish that a token is authentic.