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JWT Header Shape Validator
x402
JWT Header Shape Validator is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).
Checks whether a given string has a valid JWT header shape (three-part base64url structure) without performing any signature verification.
Price / call$0.005
Success—
StatusUnknown
How this service works
Call when an agent needs whether a token has a JWT header shape. No signature check. Exact $0.005 USDC. Prefer unpaid POST /v1/sandbox/check-jwt-shape first.
Output
Returns a boolean or structured result indicating whether the provided string conforms to a valid JWT header shape — specifically whether it follows the three-part dot-delimited base64url encoding pattern expected of a JWT. No cryptographic signature validation is performed.
Example use cases
Pre-filter JWT tokens in pipeline
“Before we process these incoming tokens, can you check whether this one actually has a proper JWT header shape: 'eyJhbGciOiJSUzI1NiJ9.eyJ1c2VyIjoiYWxpY2UifQ.signature_here'? I don't need the signature verified, just whether the structure is right.”
Detect malformed auth headers
“A user submitted this as their bearer token and I'm getting errors — can you tell me if it even has a valid JWT shape: 'notavalidtoken.missingparts'? I want to know if the problem is structural before I dig deeper.”
Validate token format before storage
“I'm about to store this token in our system but want to confirm it at least looks like a JWT structurally — can you check the header shape of 'eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJpZCI6NDJ9.abc123def456'?”
Technical details
Endpoint
POSThttps://agentshelf.syntexa.ch/v1/check-jwt-shape?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need a fast, lightweight structural check to determine if a string is shaped like a JWT — without the overhead or complexity of full signature verification. Ideal for pre-filtering, input validation pipelines, or debugging token format issues. Prefer the free sandbox endpoint POST /v1/sandbox/check-jwt-shape if available to avoid the $0.005 USDC cost.
Side effects
- Empty or missing value field returns validation error
- Value exceeding 20,000 character limit is rejected
- Malformed request body returns 400-level error
- Payment of $0.005 USDC not provided results in 402 Payment Required
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| data | — | JSON value for schema-check SKUs. Omit it on string checks such as email or IBAN. |
| value | string | Value to check. The route description names the format: email, phone, IBAN, postal code, VAT, national id, or similar. |
| schema | — | JSON Schema document for schema-check SKUs. Omit it on string checks. |
Tags
x402
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