Free Online Developer Tools
Every tool on this page runs on your machine. Paste an API response into the JSON formatter, drop a production token into the JWT decoder, or hash a customer record — nothing is uploaded, logged, or sent anywhere, which you can verify by pulling your network cable after the page loads. That matters when the string you are debugging is a bearer token or a config file you would never paste into a random site. The set covers the work that interrupts you mid-task: reformatting minified JSON, checking a regex against real input, converting between JSON, YAML, XML, and CSV, decoding percent-encoded URLs, and reading a cron expression you inherited from someone who left two years ago.
All 19 Developer Tools
JSON Formatter & Validator
Format, beautify, and validate JSON instantly. Errors with line numbers, runs 100% in your browser.
Base64 Encoder & Decoder
Encode or decode Base64 instantly with full UTF-8 and emoji support. No upload, runs in your browser.
UUID Generator (v4)
Generate random UUID v4 identifiers in bulk. RFC 4122 compliant, client-side, no signup.
Hash Generator
Compute MD5, SHA-1, SHA-256, and SHA-512 hashes from any text — all at once, in your browser.
URL Encoder & Decoder
Encode or decode URLs with percent-encoding. Choose encodeURI or encodeURIComponent. UTF-8 safe.
Regex Tester
Test and debug JavaScript regex with real-time match highlighting and capture-group colors.
Diff Checker
Compare two texts or code blocks side-by-side. Word-level highlighting, no signup, client-side.
Code Beautifier
Format and beautify HTML, CSS, and JavaScript. Expand minified files, fix indentation, copy in one click.
Cron Generator
Build cron expressions visually with plain-English descriptions and next-run preview. Supports cron, Quartz, AWS.
chmod Calculator
Set Linux file permissions visually. Numeric (755), symbolic (rwxr-xr-x), and ready-to-copy chmod command.
CSV to JSON
Convert CSV to JSON with header detection, custom delimiters, and quoted-field handling. Local-only.
JSON to CSV
Convert JSON arrays to CSV. Flattens nested objects with dot-notation columns. Excel-ready.
YAML to JSON
Convert YAML to JSON with full Kubernetes and Docker Compose support. Multi-document streams handled.
JSON to YAML
Convert JSON to clean YAML output. Anchor-friendly, Kubernetes-ready, customizable indentation.
XML to JSON
Convert XML to JSON keeping attributes and namespaces. Handles SOAP envelopes and large files.
JSON to XML
Convert JSON to XML with custom root element, attribute prefix, and pretty-print indentation.
Markdown to HTML
Convert Markdown to clean HTML with live preview. GFM tables, task lists, and code blocks supported.
JWT Decoder
Decode JWT tokens instantly. View header, payload, claims & expiration. 100% client-side.
Color Contrast Checker
Check any text and background pair against WCAG AA and AAA, with a live preview and the nearest passing colour.
Why use these developer tools
Nothing leaves your browser
Parsing, hashing, encoding, and diffing all happen in JavaScript on your device. There is no upload step and no server to log your payloads, so pasting internal data carries no more risk than opening it in your editor.
Built for real payloads
No size caps and no rate limits. Format a 5 MB API response, diff two long config files, or generate 500 UUIDs at once without hitting a paywall or a "please sign up to continue" screen.
Errors that point at the problem
When JSON fails to parse you get the line and column plus a plain-English reason, not a bare "unexpected token". The regex tester highlights matches and capture groups as you type.
Frequently asked questions
Is it safe to paste production data into these tools?
Yes, because the data never travels. Each tool uses native browser APIs — JSON.parse, TextEncoder, Web Crypto — and the result is computed locally. Load the page, disconnect from the internet, and the tools keep working. That is the simplest proof that nothing is being transmitted.
Do I need an account or an API key?
No. There is no signup, no email wall, and no key to manage. Open a tool and use it. Nothing is stored between visits either, so your inputs are gone the moment you close the tab.
Which format converters are available?
JSON to CSV, CSV to JSON, JSON to YAML, YAML to JSON, JSON to XML, XML to JSON, and Markdown to HTML. Each one round-trips, so you can convert in one direction and back to confirm nothing was lost.