Provides tools for decoding JSON Web Tokens (JWT) as well as Base64 encoded strings, enabling inspection of headers, payloads, and claims for debugging authentication and authorization flows.
Click on "Deploy Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@JWT & Base64 Decoder MCP Server decode this JWT token"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
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.
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 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.
Related MCP server: @revxl/devtools
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.
This project is built on MCP Fusion for maximum security and type safety.
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 deployVinkius Edge provides secure, stateless edge execution. We guarantee that decoded tokens are never stored, logged, or retained, ensuring strict security compliance.
If you prefer to run this locally for auditing:
npm install
npm run build
npm run devThis server cannot be deployed
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