PKCE Code Challenge Generator

Create a cryptographically random PKCE code_verifier and its S256 code_challenge with the Web Crypto API, exactly as RFC 7636 specifies. Build a ready authorization URL and token request for testing, or check that an existing verifier and challenge belong together.

Last updated: October 24, 2026

How to use the PKCE Code Challenge Generator

1. Click Generate New Pair (a pair is ready when the page loads). Adjust the verifier length if needed.
2. Copy the code_challenge and send it with code_challenge_method=S256 in the authorization request, or use the URL builder.
3. Store the code_verifier securely in your app (memory or session storage) until the user returns with an authorization code.
4. Exchange the code: send the code_verifier in the token request (see the curl example).
5. Debugging? Paste a verifier and a challenge into Verify a pair to see whether they match.

How the PKCE flow works

1. Create the verifier. The client generates a high-entropy random code_verifier (43-128 characters from A-Z a-z 0-9 - . _ ~) and keeps it secret.
2. Derive the challenge. code_challenge = BASE64URL(SHA256(code_verifier)), Base64URL without = padding.
3. Authorization request. The client redirects the user to the authorization server with code_challenge and code_challenge_method=S256. The server stores the challenge with the authorization code it issues.
4. Token request. The client sends the authorization code together with the original code_verifier.
5. Check. The server hashes the verifier and compares it with the stored challenge. Only the client that started the flow can complete it.

Test vector from RFC 7636 (Appendix B)

Click Load RFC 7636 Example to reproduce it with this tool. If your own code gives a different result, the usual culprits are standard Base64 instead of Base64URL, leftover = padding, hashing the hex string of the digest, or hashing a string that contains a trailing newline.

Generating PKCE in code

JavaScript (browser or Node 18+):

const b64url = b => btoa(String.fromCharCode(...new Uint8Array(b)))
  .replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
const verifier = b64url(crypto.getRandomValues(new Uint8Array(32)));
const challenge = b64url(await crypto.subtle.digest('SHA-256',
  new TextEncoder().encode(verifier)));

Python:

import base64, hashlib, secrets
verifier = secrets.token_urlsafe(32)  # 43 characters
challenge = base64.urlsafe_b64encode(
    hashlib.sha256(verifier.encode('ascii')).digest()).rstrip(b'=').decode()

Frequently asked questions

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