CapyToolkit

CapyToolkit is a growing collection of free browser utilities covering hardware testing, developer work, audio analysis, security and everyday personal tasks, built by a solo developer. Every tool computes locally through native browser APIs, so files and keystrokes never reach a server, and there is no install or account needed to use any tool.

Most tools are plain client-side utilities, such as a JSON formatter, a regex tester, a WCAG contrast checker and hardware diagnostics for monitors and webcams, but a few tools add AI: an Offline & Private AI Text Detector scores how AI-generated a piece of writing reads, fully offline in the browser, and a PDF to Markdown Converter uses a local AI model to handle scanned pages when converting a PDF to Markdown on the user's device.

CapyToolkit organizes its tools into categories including Hardware & Display Diagnostics, Developer Parsers & Encoders, Text Analysis Tools & Converters, Audio & Acoustic Testing, Math & Engineering Calculators, Security & Privacy Tools, Web Design Utilities and Network & Web Reference Tools, alongside personal tools such as a passport photo cropper and a local PDF toolkit. The catalog includes dozens of tools already live, with more such as a binary package differ and a WASM binary inspector listed on a public roadmap.

CapyToolkit can be installed as an app so tools stay cached locally and keep working offline, on a plane or on a locked-down network. The developer says every tool is free with no account required, no rate limit and no upgrade prompt, and plans to fund CapyToolkit in the future only through ads a visitor can switch off.

Use cases

• Checking a JWT token or JSON response for sensitive data without uploading it
• Testing a monitor for a dead pixel directly in the browser
• Splitting a receipt among people and calculating tax and tip