Free Developer & Coding Tools
Client-side utilities designed for software engineers. Format JSON, decode JWTs, test Markdown, and calculate cryptographic checksums with zero server logging.
Client-Side Developer Utilities
FastestChecker executes developer utilities directly inside your browser session using standard Web APIs, guaranteeing that API tokens, JSON payloads, and private files are never transmitted to external servers.
Available Developer Utilities
- JSON Formatter & Tree Visualizer — Format, validate, and minify JSON with collapsible tree views and CSV/YAML export.
- JWT Token Decoder & Inspector — Safely decode JSON Web Tokens (RFC 7519) offline in your browser.
- Live Markdown Editor & Previewer — Write and test GitHub Flavored Markdown (GFM) with split-pane live rendering.
- Base64 Encoder / Decoder — RFC 4648 standard binary-to-text encoding and Data URI generation.
- MD5 & SHA Hash Calculator — Compute cryptographic checksums using the native Web Crypto API.
- Binary, Decimal & Hex Converter — Convert numbers across binary, octal, decimal, and hexadecimal radices.
- Unix Timestamp Converter — Convert epoch timestamps to human UTC/local dates and back with a live clock.
- User Agent & Client Hints Inspector — Inspect your browser user-agent string, rendering engine, and Sec-CH-UA hints.
- MCP Config Generator — Generate validated JSON configs for Anthropic Claude Desktop and MCP servers.