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JWT Header Decoder (No Signature Verification)
x402
JWT Header Decoder (No Signature Verification) is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.009/call, status unknown (last checked 2026-09-29).
Decodes and returns the header portion of a JWT token without performing any signature validation
Price / call$0.009
Success—
StatusUnknown
How this service works
Call when an agent needs a decoded JWT header with no signature check. Exact $0.009 USDC. Prefer unpaid POST /v1/sandbox/jwt-header first.
Output
Returns the decoded JWT header as a JSON object containing fields such as 'alg' (signing algorithm), 'typ' (token type), 'kid' (key ID), and any other header claims present in the token, without performing any signature verification.
Example use cases
Inspect JWT signing algorithm
“I received this JWT and need to know what signing algorithm it's using before I decide how to verify it — can you decode its header? eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.payload.sig”
Debug misconfigured token header
“My service is rejecting a JWT and I suspect the header fields are wrong. Can you decode the header from this token so I can check: eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.claims.”
Extract key ID for key rotation lookup
“I need to find the kid field in this JWT header so I can look up the right public key for verification — please decode the header: eyJhbGciOiJSUzI1NiIsImtpZCI6ImtleS0yMDI0LTAxIiwidHlwIjoiSldUIn0.payload.sig”
Technical details
Endpoint
POSThttps://agentshelf.syntexa.ch/v1/jwt-header?utm_source=zero.xyzWhen to prefer
Use this endpoint when you only need to inspect JWT header metadata (algorithm, key ID, token type) without needing signature validation. Prefer this over full JWT verification libraries when you simply want to read header claims for routing, debugging, or key lookup purposes. Avoid if you need actual signature verification or payload decoding — this endpoint explicitly skips signature checks.
Side effects
- Malformed or non-JWT input string returns an error indicating invalid token format
- Empty or missing text field returns validation error
- Token with a corrupted or non-base64url-encoded header segment returns a parse error
- Extremely long token strings near the 100,000 character limit may be rejected
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| text | string | Input for this SKU. The route description says whether it is plain text, a URL, base64 bytes, or an already-encoded token. |
Tags
x402
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