JWT

Verify an ES256/ES384/ES512 JWT signature

POSThttps://ecdsa.com/api/v1/jwt/verify

Verifies the token's ECDSA signature against a public key (PEM SPKI, EC JWK, or bare SEC1 point). Non-ECDSA algorithms (HS*, RS*, PS*, EdDSA, ES256K, none) return 400 with code unsupported_algorithm. A signature that fails verification returns valid: false with HTTP 200. Time claims are noted in explanations but do not affect valid.

API key: Optional; a key needs the scope api
Quota cost with a key: 1 unit per call
Rate limit: 60 requests/min per IP

Request

JSON body: JwtVerifyRequest

Field	Type	Required	Description
token	string	yes	Compact JWS token with alg ES256, ES384 or ES512.
publicKey	string	yes	PEM "PUBLIC KEY" (SPKI), EC JWK JSON, or a bare SEC1 point in hex/base64.

Responses

200Verification outcome.

Field	Type	Required	Description
valid	boolean	yes
alg	string	yes	one of "ES256", "ES384", or "ES512"
explanations	string[]	yes

Headers: X-Request-Id · X-RateLimit-Limit · X-RateLimit-Remaining · X-RateLimit-Reset · X-Quota-Limit · X-Quota-Remaining · X-Quota-Reset

Status	Meaning	Codes
400	Bad request. Input limits: a request body of at most 100 KB (a larger one is answered with 413) and arrays and objects nested at most 64 levels deep, JSON documents inside string fields included.	invalid_json missing_field invalid_input private_key_rejected unsupported_algorithm
401	Unauthorized.	unauthorized
403	Forbidden.	forbidden_scope
404	Not found.	not_found
405	Method not allowed.	method_not_allowed
413	Payload too large.	payload_too_large
429	Too many requests.	rate_limited quota_exceeded
500	Internal server error.	internal_error
503	Service unavailable.	service_unavailable
504	Gateway timeout.	timeout

Every error answer carries the JSON envelope; the error table says what each code means and what to do.

Example

An ES256 token and its public JWK

curl

curl -sS 'https://ecdsa.com/api/v1/jwt/verify' \
  -H 'content-type: application/json' \
  -d '{
  "token": "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImNvcHBlci1leGFtcGxlLTEifQ.eyJpc3MiOiJodHRwczovL2lzc3Vlci5leGFtcGxlLmNvbSIsInN1YiI6InVzZXJfNDIiLCJhdWQiOiJlY2RzYSIsImlhdCI6MTc4NzE0MDgwMCwiZXhwIjo0MDcwOTA4ODAwfQ.fQpTQxkahGRlZp-U71-xNk68mpZH23dhn9QoysMLmZfBx_e-vd9sCgh7sJ4eXu0-WbQSNqzmVPyUKErCJx4DHw",
  "publicKey": "{\n  \"kty\": \"EC\",\n  \"crv\": \"P-256\",\n  \"x\": \"A4KIXkvTVuOzkR5Mzgsy8n_VSSIlephF1ViMxDYTUx4\",\n  \"y\": \"Py8AMAM_6yWsOTbv8eHCvKDfObpZmTHy5P4Jz30iMuU\",\n  \"kid\": \"copper-example-1\"\n}"
}'

JavaScript (fetch)

const response = await fetch("https://ecdsa.com/api/v1/jwt/verify", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "token": "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImNvcHBlci1leGFtcGxlLTEifQ.eyJpc3MiOiJodHRwczovL2lzc3Vlci5leGFtcGxlLmNvbSIsInN1YiI6InVzZXJfNDIiLCJhdWQiOiJlY2RzYSIsImlhdCI6MTc4NzE0MDgwMCwiZXhwIjo0MDcwOTA4ODAwfQ.fQpTQxkahGRlZp-U71-xNk68mpZH23dhn9QoysMLmZfBx_e-vd9sCgh7sJ4eXu0-WbQSNqzmVPyUKErCJx4DHw",
    "publicKey": "{\n  \"kty\": \"EC\",\n  \"crv\": \"P-256\",\n  \"x\": \"A4KIXkvTVuOzkR5Mzgsy8n_VSSIlephF1ViMxDYTUx4\",\n  \"y\": \"Py8AMAM_6yWsOTbv8eHCvKDfObpZmTHy5P4Jz30iMuU\",\n  \"kid\": \"copper-example-1\"\n}"
  }),
});
console.log(response.status, await response.json());

Python (httpx)

import httpx

response = httpx.post(
    "https://ecdsa.com/api/v1/jwt/verify",
    json={
        "token": "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImNvcHBlci1leGFtcGxlLTEifQ.eyJpc3MiOiJodHRwczovL2lzc3Vlci5leGFtcGxlLmNvbSIsInN1YiI6InVzZXJfNDIiLCJhdWQiOiJlY2RzYSIsImlhdCI6MTc4NzE0MDgwMCwiZXhwIjo0MDcwOTA4ODAwfQ.fQpTQxkahGRlZp-U71-xNk68mpZH23dhn9QoysMLmZfBx_e-vd9sCgh7sJ4eXu0-WbQSNqzmVPyUKErCJx4DHw",
        "publicKey": "{\n  \"kty\": \"EC\",\n  \"crv\": \"P-256\",\n  \"x\": \"A4KIXkvTVuOzkR5Mzgsy8n_VSSIlephF1ViMxDYTUx4\",\n  \"y\": \"Py8AMAM_6yWsOTbv8eHCvKDfObpZmTHy5P4Jz30iMuU\",\n  \"kid\": \"copper-example-1\"\n}",
    },
    timeout=30.0,
)
print(response.status_code, response.json())

Response 200

{
  "valid": true,
  "alg": "ES256",
  "explanations": [
    "ES256: ECDSA on P-256 with SHA-256; the JWS signature is raw r‖s (64 bytes) over the ASCII bytes of base64url(header).base64url(payload).",
    "The signature verifies with the supplied key."
  ]
}

The API’s answer to this example, produced for this page on October 20, 2026; relative times and day counts in it refer to that day.

Error codes

Code	Status	Meaning
invalid_json	400	The body is not valid JSON or not a JSON object; or the input nests arrays and objects more than 64 levels deep (JSON documents inside string fields count too), or is too complex to inspect for private keys.
missing_field	400	A required field is absent or empty.
invalid_input	400	A field could not be parsed — the message explains exactly why.
private_key_rejected	400	The request contains private-key material (a PEM PRIVATE KEY block, an OpenSSH, SSH2 or PuTTY private key, or a JWK with "d"). Never send private keys anywhere.
unsupported_algorithm	400	The token's algorithm is not one this operation verifies.
unauthorized	401	The Authorization or X-API-Key header is malformed, the API key is not valid (wrong checksum, unknown, revoked or expired), or the operation needs a key.
forbidden_scope	403	The API key is valid but lacks a scope this operation requires; the message names it.
not_found	404	No operation exists at this path.
method_not_allowed	405	The path exists but does not accept this HTTP method; see the Allow header.
payload_too_large	413	The body exceeds 100 KB.
rate_limited	429	Too many requests — see Retry-After.
quota_exceeded	429	A daily or monthly quota of the API key's account is used up. X-Quota-Reset (and Retry-After) say when it starts over; retrying earlier cannot succeed.
internal_error	500	Unexpected server error.
service_unavailable	503	API keys cannot be verified right now (the key store is unreachable); retry shortly.
timeout	504	The operation did not finish within its time budget.

Schemas

Error

The error envelope of every non-2xx response.

Field	Type	Required	Description
error	object	yes
error.code	string	yes	Machine-readable error code. Each response lists the codes it can carry; new codes may be added within v1, so treat an unknown code by its HTTP status.
error.message	string	yes	Human-readable explanation (English).
error.requestId	string	no	The X-Request-Id of this request — quote it when reporting a problem. Sent since v1.1.
error.detail	object	no	Structured context for the error, such as the offending field; omitted when there is none. any member names
error.docs	string	no	Where the error codes are explained. Sent since v1.1. format uri

All operations are listed in the API reference.