How to sign a JWT with ES256 in Python

1import time
2 
3import jwt  # PyJWT; ES256 needs the cryptography package: pip install "pyjwt[crypto]==2.15.1"
4 
5with open("key.pem") as f:
6    private_key = f.read()  # PEM text; PyJWT loads it with cryptography
7 
8now = int(time.time())  # whole seconds, as NumericDate expects
9token = jwt.encode(
10    {
11        "iss": "https://issuer.example.com",
12        "sub": "user-42",
13        "aud": "api://orders",
14        "iat": now,
15        "exp": now + 15 * 60,
16    },
17    private_key,
18    algorithm="ES256",
19    headers={"kid": "2026-10"},
20)
21print(token)
22 

How it works

1. jwt.encode accepts the PEM text directly (PKCS#8 or EC PRIVATE KEY) and loads it with cryptography.
2. headers={"kid": "2026-10"} adds the key id; PyJWT always writes alg and typ itself.
3. iat and exp are integers here; a datetime also works and is converted to whole seconds.
4. PyJWT 2.x returns the token as str (1.x returned bytes), so it can be printed or put in a header as is.

Gotchas

• Plain pip install pyjwt cannot sign ES256: NotImplementedError: Algorithm 'ES256' could not be found. Do you have cryptography installed?. Install pyjwt[crypto].
• The key must match the algorithm: a P-384 key with algorithm="ES256" raises InvalidKeyError: The key's curve 'secp384r1' does not match the expected curve 'secp256r1' for this algorithm.
• Passing the public key, or the PEM as a secret for HS256, is a different mistake with a different error — see the related error pages; ES256 always signs with the private key.
• jwt.encode does not add exp or iat on its own. A token without exp never expires, and most verifiers accept it unless told to require the claim.

Related recipes

• How to verify an ES256 JWT in Python
• How to verify a JWT with a JWKS in Python
• How to compute a JWK thumbprint (RFC 7638) in Python
• How to sign a JWT with ES256 in Node.js
• How to sign a JWT with ES256 in Go