JWT & Base64 Decoder MCP Server

An essential cybersecurity and debugging Model Context Protocol (MCP) server that empowers AI agents to safely parse, decode, and inspect JSON Web Tokens (JWT) and Base64 encoded payloads in real-time.

Why AI Agents Need Native Decoding

When an autonomous agent is debugging an authentication failure or analyzing a network trace, it frequently encounters JWTs and Base64 encoded strings. LLMs cannot natively decode Base64. Because tokenizers break Base64 strings into meaningless sub-word tokens, the AI cannot "read" the underlying payload. If an LLM attempts to guess the contents of a JWT based on the encoded string, it relies purely on hallucination.

The Solution: Deterministic Inspection

The JWT & Base64 Decoder MCP solves this critical blind spot. By passing the encoded string to this server, the agent receives the exact, deterministically parsed JSON header, payload, and signature metadata. This allows the AI to accurately diagnose token expiration, scope issues, and malformed claims without guessing.

Tool Capabilities

• decode_jwt

  • Function: Safely parses a JWT, returning the decoded header and payload (claims) without verifying the signature (safe for inspection).
  • Use Case: Debugging OAuth flows, identifying expired tokens (exp claim), and auditing user roles.

• decode_base64

  • Function: Strictly decodes Base64/Base64URL strings back into UTF-8 text or hex representation.

Run on Vinkius Cloud & Open-Source Architecture

This project is built on MCP Fusion for maximum security and type safety.

1. Free Edge Hosting (Recommended)

Attach this critical debugging capability to your agents instantly without managing infrastructure. Vinkius provides FREE, highly available edge hosting for MCP servers.

👉 Connect the JWT Decoder MCP via Vinkius

Alternatively, you can deploy this exact server in seconds:

npx mcpfusion deploy

Vinkius Cloud provides secure, stateless edge execution. We guarantee that decoded tokens are never stored, logged, or retained, ensuring strict security compliance.

2. Local Development

If you prefer to run this locally for auditing:

npm install
npm run build
npm run dev