# FastX402 Lab JWT Decoder

> FastX402 Lab JWT Decoder is a paid API for AI agents from fastx402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-17).

Decodes a JWT's header and payload, reporting algorithm, issue/expiry times, expiration status, and seconds until expiry — without verifying the signature.

## Facts

- Endpoint: GET https://fastx402.tools/jwt-decode?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastx402-lab-jwt-decoder-a7509926
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_w4daM7baL5pwT6WhJ5cEj

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability fastx402-lab-jwt-decoder-a7509926
```

Example prompt: Can you decode this JWT for me and tell me whether it's expired, when it was issued, and what signing algorithm it uses? Token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ1c2VyLTEyMyIsImlhdCI6MTc5MDAwMDAwMCwiZXhwIjoxNzkwMDAzNjAwfQ.abc123

## When to prefer this

Choose this endpoint when you need to quickly inspect JWT claims, algorithm, or expiration status during debugging or automation — especially when signature verification is unnecessary or the secret/key is unavailable. It is ideal for lightweight token inspection in CI pipelines, agent auth flows, or log analysis. Prefer a full JWT verification library when you actually need cryptographic signature validation.

## Known failure modes

- Malformed or non-JWT string causes a parse error response
- Missing required 'token' query parameter returns a validation error
- Token with no expiry claim (no 'exp') may return null or zero for expiry-related fields
- Network or payment failure returns a 402 or 5xx response

## How this service works

146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.

## Output

Returns a JSON object containing the decoded JWT header (alg, typ), the decoded payload (sub, iat, exp, plus any other claims), the algorithm string, human-readable issued_at and expires_at timestamps in ISO 8601, an expired boolean, whether a signature is present, and the number of seconds until expiry (negative if already expired).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "token"
     ],
     "properties": {
      "now": {
       "type": "string",
       "description": "Optional: current time as unix seconds, for a reproducible answer"
      },
      "token": {
       "type": "string",
       "description": "The JWT"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "header": {
       "type": "object",
       "properties": {
        "alg": {
         "type": "string"
        },
        "typ": {
         "type": "string"
        }
       }
      },
      "expired": {
       "type": "boolean"
      },
      "payload": {
       "type": "object",
       "properties": {
        "exp": {
         "type": "integer"
        },
        "iat": {
         "type": "integer"
        },
        "sub": {
         "type": "string"
        }
       }
      },
      "algorithm": {
       "type": "string"
      },
      "issued_at": {
       "type": "string"
      },
      "expires_at": {
       "type": "string"
      },
      "signature_present": {
       "type": "boolean"
      },
      "seconds_until_expiry": {
       "type": "integer"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "header": {
   "alg": "HS256",
   "typ": "JWT"
  },
  "expired": false,
  "payload": {
   "exp": 1790003600,
   "iat": 1790000000,
   "sub": "agent-42"
  },
  "algorithm": "HS256",
  "issued_at": "2026-09-21T14:13:20Z",
  "expires_at": "2026-09-21T15:13:20Z",
  "signature_present": true,
  "seconds_until_expiry": 1800
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastx402-lab-jwt-decoder-a7509926/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fastx402.tools](https://www.zero.xyz/host/fastx402.tools/llms.txt)