Castov Offline JWT Decoder vs jwt.io — Zero-Telemetry Token Inspector
Compare Castov's 100% offline JWT Decoder (Browser, CLI `npx castov jwt`, and MCP tool `castov_jwt_decode`) against jwt.io for inspecting production bearer tokens safely.
Pasting production Bearer tokens into third-party websites triggers security alerts at many organizations. Castov provides a strict zero-telemetry browser JWT inspector plus a terminal CLI (`npx castov jwt <token>`) and MCP tool (`castov_jwt_decode`) that never make external network requests.
Feature-by-Feature Comparison: Castov vs. jwt.io
| Capability / Dimension | Castov (v1.4.0) | jwt.io |
|---|---|---|
| Terminal CLI Inspection (`npx castov jwt`) | Yes — decode header, payload & expiration directly in terminal without opening a browser | Web-only interface (no official zero-dependency npx CLI) |
| Native AI Agent MCP Tool (`castov_jwt_decode`) | Yes — AI agents inspect exp/iat claims locally via stdio JSON-RPC | None |
| Third-Party Analytics / Trackers | Zero third-party telemetry; works 100% offline / air-gapped | Commercial property (Auth0/Okta) with marketing banners & scripts |
| Automatic Unix Timestamp (`exp`, `iat`, `nbf`) Diff | Instant human-readable ISO-8601 + expired/active status badge | Requires hover or manual epoch conversion |
| Language Library Directory | Focused on fast token decoding, epoch math, and secret generation | Extensive directory of third-party JWT libraries across 20+ languages |
When to Choose Castov
- You need to inspect a staging or production JWT directly in your terminal (`npx castov jwt <token>`) without copying sensitive tokens into a web browser.
- Your AI assistant (Claude/Cursor) needs to debug token expiration (`exp`/`iat`) locally via `castov_jwt_decode`.
- You want a clean, fast browser JWT decoder linked directly to Unix timestamp and cryptographic secret generators.
When to Keep jwt.io
- You are browsing a catalog of language-specific JWT verification libraries (Java, C#, PHP, Ruby).
How to Run Castov in 60 Seconds (Zero Config)
Decode JWTs Directly in Your Terminal
Run `npx castov jwt <YOUR_JWT_TOKEN>` to view decoded header, payload claims, and expiration timestamps locally.
Enable JWT Debugging in Claude & Cursor
Configure `npx -y castov@latest mcp` in your IDE so your AI agent can call `castov_jwt_decode` without uploading tokens.
Use the Offline Browser Inspector
Bookmark `https://www.castov.com/jwt-decoder` for instant client-side inspection with automatic `iat`/`exp` date conversion.
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