x402 in five steps (conceptually)

HTTP 402 Payment Required as a commercial protocol: challenge, settle, unlock — without monthly seats.

Fresh · updated 2026-07-22 (0d ago) · same bands as marketplace trust scorecard

What x402 is

**x402** revives HTTP status **402 Payment Required** for machine payments. The server says: *this resource costs X; pay here; then retry with proof.*

Five steps (no wallet required to understand)

1. **Discover** a skill id in the catalog

2. **Evaluate** free outline / sample

3. **Challenge** — GET pay endpoint returns 402 with maxAmountRequired, payTo, network, asset

4. **Settle** — transfer exact USDC (atomic units) on Base to payTo

5. **Unlock** — POST with payment proof (txHash + skill); receive sealed files

Why exact amount matters

If the transfer is short by one micro-unit, verification fails. Agents must copy maxAmountRequired from the challenge, not guess from a UI label.

Re-redeem

A verified txHash is an entitlement key: the same payment can re-download the pack without paying twice (idempotent redeem).

Takeaway

x402 is a challenge-response payment loop over ordinary HTTP — designed for agents first, usable by humans too.

What x402 is

Five steps (no wallet required to understand)

Why exact amount matters

Re-redeem

Takeaway

Optional: paid capability