JWT Decoder API

io.github.Br0ski777Published by GitHub account Br0ski777v1.1.0Updated Nov 2, 2026

Decode JWT tokens — inspect header, payload, claims, expiry. x402 micropayment.

VerifiedSSEWeb executableDeveloper ToolsSecurity & Monitoring

Overview

AI-generated overview

Remote MCP endpoint that decodes JWT tokens, returning header, payload, claims and expiry status, paid per call via x402 micropayments.

What you can do
  • Decode a JWT token and return its header, payload, claims, signature algorithm and expiration status
  • Inspect whether a token is expired and when it was issued or expires, without verifying the signature
  • Use the result to debug authentication problems or check whether a token needs refreshing before an authenticated request
When to use it
Useful when an assistant needs to inspect a JWT's claims or expiry while debugging authentication, or before making authenticated API calls. It only decodes; it does not verify signatures or handle hashing, base64 or password checks.
Requirements
A remote MCP endpoint reached over SSE at the provider's URL; no API key, signup or environment variables. Each call is paid per use in USDC on Base L2 through the x402 protocol, so an x402-aware client with a funded wallet is needed to handle the payment challenge.
Before you install
Every call costs money (listed at $0.003 per decode) in USDC on Base, so an agent can spend funds automatically. The token is sent to a third-party service, and decoded payloads may contain sensitive claims; the service does not verify signatures, so results say nothing about authenticity.

Installation

In SourceWeft

  1. Open JWT Decoder API in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via SSE. Remote servers run from the web runtime once configured in a workspace.

Use with an agent

Paste this prompt into Claude Code, Codex, Cursor or another agent — or into SourceWeft chat. The agent reads this server's install guide, shows you its publisher, endpoint and sign-in, and adds it to your client once you agree. Keys never go into a command.

Read https://sourceweft.com/mcp/io.github.Br0ski777%2Fjwt-decoder/install.md and connect the MCP server it describes to my client. Before changing any config, show me its publisher, endpoint and sign-in method and wait for my OK. Never put an API key in a command or in a file I would commit; ask me where it should come from.

Read the install guide the agent follows

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "jwt-decoder-api": {
      "type": "sse",
      "url": "https://jwt-decoder.api.klymax402.com/mcp"
    }
  }
}

README

JWT Decoder API

[MCP Server] [x402] [License: MIT]

Decode and inspect JWT tokens without verification. Extracts header, payload, claims, expiry, and signature algorithm. Pay-per-call via x402 (USDC on Base L2) -- no API key, no signup, no rate-limit wall.

Part of the klymax402 marketplace -- 100 x402 micropayment APIs for AI agents, one wallet, USDC on Base.

Quickstart -- MCP

Add to your MCP client config (Claude Desktop, Cursor, ElizaOS, etc.):

json
{  "mcpServers": {    "jwt-decoder": {      "url": "https://jwt-decoder.api.klymax402.com/mcp"    }  }}

Quickstart -- HTTP (x402)

bash
curl -X POST "https://jwt-decoder.api.klymax402.com/api/decode" \  -H "Content-Type: application/json" \  -d '{"token":"..."}'# -> 402 Payment Required, with an x402 payment challenge in the response body

Any x402-aware client (@x402/fetch, x402-agent-tools, ATXP) handles the 402 -> sign -> retry cycle automatically.

Tools

ToolMethodPathPriceDescription
security_decode_jwtPOST/api/decode$0.003Decode a JWT token without signature verification

security_decode_jwt

Use this when you need to decode and inspect a JWT token without verifying its signature. Returns the full header, payload, and expiration status.

Parameters

NameTypeRequiredDescription
tokenstringyesThe JWT token to decode (format: header.payload.signature)

Example response:

json
{"header":{"alg":"RS256","typ":"JWT"},"payload":{"sub":"user123","exp":1720000000},"issuedAt":"2025-01-01T00:00:00Z","expiresAt":"2025-07-03T00:00:00Z","isExpired":false}

When to use: debugging authentication issues, inspecting token claims before API calls, or verifying token expiry. Use this BEFORE making authenticated requests to check if a token needs refreshing.

Not for: hashing data (use crypto_generate_hash), base64 encoding/decoding (use utility_encode_base64), password analysis (use security_check_password).

Example agent prompts

  • "Decode and inspect a JWT token without verifying its signature"

Payment

  • Protocol: x402 -- HTTP-native pay-per-call, no signup, no API key
  • Network: Base L2 (eip155:8453)
  • Asset: USDC
  • Facilitator: Coinbase CDP (primary), PayAI (fallback)
  • Also reachable via ATXP (OAuth-wrapped x402, RFC 9728 protected-resource metadata)

Part of klymax402

100 x402 micropayment APIs for AI agents -- one wallet, USDC on Base, zero signup.

License

MIT

Source: README.md at commit 3593930

Tools

0
SourceWeft has not read this server's tools yet.

Version history

1
  1. v1.1.0LatestSep 16, 2026

Score

50% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

  • Reached in the last 30 daysRequired25 pts

    Keep the endpoint answering the MCP handshake; SourceWeft probes it every 30 days.

  • Auth declaredRequired10 pts

    Declare the credential headers in the registry entry, or keep the endpoint answering the probe so its auth can be classified.

  • Tools listed15 pts

    Answer tools/list without a credential, or ship a package that starts in a sandbox without one.

  • DescriptionRequired15 pts
  • Logo10 pts
  • Documentation15 pts
  • License10 pts