Free developer tools
A growing collection of browser-only utilities for developers. Decode tokens, generate IDs, hash files, test patterns, convert between formats. Nothing leaves your machine - everything runs in the page.
Encode and decode
Decode and inspect JSON Web Tokens. Standard claims annotated, expiry flagged, header and payload pretty-printed.
Encode and decode Base64 (standard and URL-safe) with full UTF-8 support, swap button, suggestion detection.
One page, four targets. Escape and unescape strings for URLs, HTML, JS literals, and JSON literals.
Generate and inspect
v4, v7, v1, NIL. Bulk up to 1000. Inspector reads back version, variant, and embedded timestamp.
Convert Unix epoch to and from dates. Live "now" ticker, seven time zones, seconds vs ms auto-detect.
MD5, SHA-1, SHA-256, SHA-384, SHA-512. Text or file. Hex, Base64, or Base64URL output.
Live JavaScript regex playground. Flag toggles, named and numbered groups, substitution preview.
Parse 5-field cron expressions. Human-readable description plus the next 10 fire times in local and UTC.
Convert
Paste a curl command, get the equivalent JavaScript fetch and axios. Live, edit-friendly output.
Round-trip JSON and YAML. Edit either pane, the other updates live. Inline parse errors.
Convert arrays of JSON objects to CSV and back. Configurable delimiter, header row, and quoting.
Format and edit
Pretty-print, minify, and validate JSON with line / column error context.
Format and minify JavaScript source.
Pretty-print, minify, and validate XML.
Parse, simulate, and explain G-code for CNC and 3D printers.
8x8 and 16x16 LED matrix editor with animation timeline and byte export.
Why browser-only?
Most "free online tool" sites POST your input to a server before showing you a result. That's fine for a JSON formatter, less fine for a JWT, hash, or anything else where the input might contain secrets or PII. Every tool on this page runs entirely in your browser using native Web APIs (and, where the API is missing, a small vendored library checked for CSP-safety). The page makes no network calls during the computation; your tokens, your files, and your test data stay on your machine.
Built on what we run ourselves
Go REST is a public REST API service for fake data and a working REST playground. These tools are the side bench - the things we reach for when we're debugging a request, prepping a fixture, or reading a config. We ship them here so other developers can use the same set without a sign-up or a billing page.
Suggest a tool
If there's a tool you wish existed here, drop a note via thecontact form. Common asks so far: SQL formatter, Markdown preview, image-size optimizer, and a public-key inspector. They're on the roadmap; the order depends on what people actually ask for.