Developer Tools
Small utilities for the everyday parts of writing and debugging code — reading a JSON response, decoding a token, or encoding a string for a URL — without opening a full IDE or pasting data into a random website.
Base64 Encode/Decode
UTF-8 safe Base64 encoding and decoding with instant validation.
OpenColor Picker/Converter
Convert HEX, RGB and HSL, pick a color visually, and check WCAG contrast ratios.
OpenCron Expression Explainer
Explain a cron schedule in plain English and show its next run times.
OpenCSV ↔ JSON Converter
Convert spreadsheet CSV data and JSON arrays back and forth, with type inference.
OpenHTML Formatter
Beautify or minify HTML, with script/style/pre content always left untouched.
OpenJSON Viewer
Paste, format, validate, and inspect JSON with a collapsible local tree view.
OpenJWT Decoder
Paste a JWT to see its decoded header and payload, with claim timestamps humanized.
OpenMarkdown Previewer
Live preview of GitHub-flavored Markdown, with tables, task lists, and a Copy HTML button.
OpenRegex Tester
Test regex patterns with live match highlighting, capture groups, and a replace preview.
OpenSQL Formatter
Beautify SQL queries with dialect-aware formatting and keyword casing.
OpenText & JSON Diff Checker
Line-by-line text diff, with a JSON mode that ignores formatting and key order.
OpenURL Encode/Decode
Percent-encode or decode full URLs or individual query components.
OpenYAML ↔ JSON Converter
Convert config files between YAML and JSON, including multi-document YAML.
OpenMost developer tools online ask you to paste sensitive data — an API response, an auth token, a config file — into a form that gets sent to someone else's server. Every tool on this page runs entirely in your browser's JavaScript engine. Nothing you paste in ever leaves your device, which matters more than it sounds like the first time you go to decode a production JWT and realize you don't actually know where that pasteboard site sends your data.
The tools here cover the formats developers actually run into daily: JSON (viewing and validating API responses or config files), Base64 (encoding binary-ish data for URLs, headers, or embedding), URL encoding (safely passing special characters in query strings), and JWT (inspecting the header and payload of a token without needing the signing key).
Each one is a single-purpose page — no sign-up, no rate limit, no ads interrupting the work. Open it, do the one thing, close the tab.
What you can use it for
- Pretty-print a minified JSON API response to actually read it
- Validate that a JSON payload is well-formed before sending it in a request
- Decode a JWT to check its expiry, claims, or issuer without a backend
- Base64-encode a string for a Basic Auth header or a data URI
- URL-encode a query parameter that contains spaces, & or other reserved characters
Frequently asked questions
Is it safe to paste API keys or tokens into these tools?
Yes — none of the developer tools on this page send data to a server. JSON formatting, Base64 encoding, URL encoding, and JWT decoding all run as JavaScript in your own browser tab. You can even disconnect from the internet after the page loads and they will keep working.
Can the JWT decoder verify a token's signature?
No. It decodes and displays the header and payload — the parts you can read without a secret key — but signature verification needs the signing key, which only your backend should have. Use it to inspect claims, not to authenticate a request.
What's the difference between Base64 encoding and encryption?
Base64 is not encryption — it's a reversible encoding that turns binary data into text-safe characters. Anyone can decode it instantly. Never use Base64 alone to protect a password or secret.
Do I need to install anything?
No. Every tool here is a web page — works on desktop or mobile, any modern browser, no extension or app required.