x402-inspect

Decode and validate x402 protocol messages from the command line.

x402 is an open payment protocol for the internet (HTTP 402), used for agent and machine payments. Its messages ride as base64-encoded JSON in three headers:

When something rejects your payment, you're usually staring at an opaque base64 blob. x402-inspect decodes it, tells you which message it is, and checks it against the v2 spec — required fields, EVM address / amount / timestamp / nonce / signature shape, CAIP-2 network — so you can see what's actually wrong fast.

Install

pip install x402-inspect

Usage

# paste a header value (base64) or raw JSON
x402-inspect "eyJ4NDAyVmVyc2lvbiI6Mi..."

# or pipe it
echo "$PAYMENT_SIGNATURE" | x402-inspect

# machine-readable
x402-inspect --json "$header"

Example:

$ x402-inspect "$header"
kind:     PaymentPayload
encoding: base64
findings:
  [warn] payload.signature: not a 65-byte 0x EVM signature
  [FAIL] payload.authorization.value: required field missing
result:   INVALID

Exit code is 0 when valid, 1 when invalid — usable in CI or a pre-flight check.

Library

from x402_inspect import inspect
rep = inspect(header_value)          # base64 or JSON
print(rep.kind, rep.ok)
for f in rep.findings:
    print(f.level, f.path, f.message)

Scope

• v2 spec (v1 X-PAYMENT header name tolerated).
• Deep validation for the exact / EVM scheme; other schemes/networks are structurally checked and flagged as warnings rather than failures (so a Solana or future-scheme payload still inspects, it just won't over-assert EVM shape).
• Validation only — it never verifies signatures on-chain or contacts a facilitator.

License

MIT