Works OfflineZero CloudNo AccountAlways Free

Tools that run
in your browser.

Hardware tests, developer utilities, audio analysis, engineering calculators — computed locally using browser-native APIs. Zero cloud. Your files and keystrokes never reach a server.

Recent Tools

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In development

Tool Planned Release
JSON Formatter & Validator Pretty-print, minify, and validate JSON with syntax highlighting.
2026-06
Live Signal Debugger Visualize real-time USB/Serial/Bluetooth signals from Arduino, sensors, and MIDI controllers — WebSerial-based, zero install.
2026-06
Markdown Preview Live-render Markdown with clean typeset output and copy-as-HTML export.
2026-06
Reading Time Calculator Paste any text and get reading time at adjustable WPM targets.
2026-06
Regex Tester Test regular expressions with live match highlighting and group capture view.
2026-06
UUID Generator Cryptographically random UUID v4 generation with bulk export.
2026-06
WCAG Contrast Checker AA and AAA contrast ratio testing with hex, RGB, and HSL input.
2026-06
Binary Package Differ Diff two ZIP archives or build artifacts in-browser — file-level tree view, size delta, and byte-level changes. Zero upload.
2026-07
Build Integrity Verifier Verify reproducible builds by hashing two local artifacts with SHA-256 and BLAKE3, then deep-diffing functional content. Zero upload.
2026-07
Local Secret Scanner Scan code, configs, and ZIP archives for leaked API keys, tokens, and credentials — regex rule engine, zero upload, nothing sent anywhere.
2026-07
Quantum-Safe Encryptor Encrypt and decrypt text with post-quantum cryptography (Kyber/Dilithium via WASM) — plaintext never leaves your browser.
2026-07
Text / Code Diff Viewer Side-by-side and unified diff with line-level highlighting.
2026-07
WASM Binary Inspector Inspect and decompile WebAssembly binaries to WAT in your browser — memory map, exports, imports, zero upload.
2026-07
WebUSB Hardware Flasher Flash firmware to ESP32, Arduino, and Raspberry Pi Pico directly in your browser — no IDE or drivers required.
2026-07

Why this matters

Hardware tests require local execution

No server can detect a dead pixel at coordinate (1847, 932) on your monitor. That class of test is physically impossible to run remotely. The browser runs it directly on your GPU.

Sensitive data stays on your machine

JWT tokens contain user roles and emails. JSON responses often include PII. Pasting those into a random online formatter is a security decision most people make without thinking.

The page is the application

No cold-start, no hydration waterfall, no API round-trip. Open it, use it, close it.

Free tools with no business model friction

No account required. No rate limit. No "upgrade to pro" modal. These are browser primitives — the right cost for them is zero.

Works Offline

Your toolkit, cached and ready.

Install CapyToolkit as an app and your browser caches every tool to your device. Dead pixel test on a plane, JWT decoder in a secure lab — no connection required. Bookmark it and you'll always have a one-click shortcut back, whether you reach for it tomorrow or six months from now.