Free Online Developer tools
Formatters, decoders, testers and checkers for the things developers paste all day — JSON, tokens, regexes, diffs, CSVs. Every tool on this page runs entirely in your browser tab: nothing you paste is sent to a server, because there is no server-side code to receive it. Open the Network tab and watch; after the page loads, nothing further leaves your machine.
- 01JSON Formatter & ValidatorBeautify, validate, minify — with line and column.
- 02JWT DecoderRead header and payload. Never logged.
- 03Color ConverterConvert HEX, RGB and HSL colours.
- 04Text Diff CheckerAdded, removed and unchanged lines, highlighted.
- 05CSV to JSON ConverterBoth ways, quoted fields handled properly.
- 06Unix Timestamp ConverterEpoch and human dates, UTC and local.
- 07HTML Entity Encoder & DecoderEscape or decode angle brackets, quotes, non-ASCII.
- 08Regex TesterLive match highlighting and capture groups.
- 09File Hash & Checksum VerifierCheck a download really is what was published.
- 10LLM Token CounterCount tokens and compare API costs, in your browser.
Most of the work on this page is reading something a machine produced. The JSON Formatter & Validator beautifies, validates or minifies a blob, and when the input will not parse it reports the exact line and column of the failure, so you fix the offending character instead of scanning for it. The JWT Decoder splits a token at its two dots and Base64url-decodes the header and payload, so you can read who the token is for and when it expires. The CSV to JSON Converter works in both directions and handles quoted fields properly, so a comma inside quotes does not split the row.
Two more are for probing and comparing your own text. The Regex Tester highlights matches and capture groups live as you edit the pattern, against text you paste in — which means you can test against real log lines rather than sanitized stand-ins. The Text Diff Checker marks added, removed and unchanged lines; the things worth diffing — configs, contracts, code under review — are usually the things you least want in a stranger's logs. And the File Hash & Checksum Verifier reads a downloaded file in your tab, computes its SHA-1, SHA-256, SHA-384 or SHA-512 digest, and lets you compare it against the one the publisher lists, without the file ever leaving your machine.
The distinction that matters: a typical online formatter or decoder is a form. Your input is posted to a server, processed there and sent back, and a copy can sit in that server's logs indefinitely. Pasting a production JWT, or an API response with keys still in it, into one of those is a real security incident — a valid token in someone else's logs is a live credential for as long as it is valid. These tools have no server side. Each page is a static file served from a CDN, and the parsing, matching, diffing and hashing all happen in JavaScript inside your tab.
You do not have to take that on faith. Open your browser's developer tools, switch to the Network tab, and use any tool here. You will see the page and its assets load, and then nothing further — no request carrying your token, your data or your text. The stronger test: load a tool page, turn off your Wi-Fi, and keep using it. Every tool on this page keeps working. There is no sign-up, no usage limit, and nothing to pay.