Interline — agent-to-agent payment router
Archived (2026-10-10). Interline is no longer maintained. The code stays here for reference; nothing is being developed, and the testnet demos are not monitored.
An agent-to-agent payment router: one agent does work, another agent pays for it, no human keys a card. Interline is a neutral, non-custodial router over the fragmented agent-payment-rail stack — "OpenRouter for agent payments." Built on x402 (HTTP-402 micropayments, USDC), aggregator-shaped so adding a rail is one adapter, not a rewrite.
Today it routes payments across three live rails — x402 USDC on EVM
(Base Sepolia) and on Solana (devnet), plus MPP on Tempo (Moderato testnet) —
all behind one Paywall.gate() call. Real on-chain agent-to-agent settles are
confirmed on all three. It ships an MCP router so agents can discover + pay
endpoints, and includes a Google-AP2 inbound adapter — a signed AP2 mandate
(verified, constraint-checked + freshness-gated) settles non-custodially on the rails.
Run the demo (no wallet, no faucet, no risk)
python3 -m venv .venv && source .venv/bin/activate
pip install -r requirements.txt
python3 run_demo.py
Expected: DEMO PASS — agent paid agent, settlement receipt issued.
What just happened (the x402 "exact-evm" loop):
buyer GET /work
-> seller 402 + PaymentRequirements {amount, asset=USDC, payTo, network}
-> buyer signs an EIP-3009 transferWithAuthorization (gasless USDC auth)
-> buyer retries with X-PAYMENT header (base64 signed payload)
-> facilitator VERIFIES the signature (real signer-recovery) + checks policy
-> facilitator SETTLES (mock: fake tx hash; live: on-chain USDC transfer)
-> seller 200 + work product + X-PAYMENT-RESPONSE receipt (tx hash)
The facilitator's verify step is real cryptography even in mock mode — it recovers the EIP-712 signer and matches it to the authorization. Only the on-chain broadcast is mocked. So a passing demo proves the buyer's signing is protocol-correct against real USDC.
Files
| file | role |
|---|---|
router/paywall.py | the reusable Paywall primitive — gate any endpoint behind x402 in one .gate() call |
router/ledger.py | settlement receipt-ledger → logs/agent_payment_settlements.jsonl (audit trail) |
router/seller.py | FastAPI agent that sells work — defines the requirements + work, wires one Paywall.gate() |
router/buyer.py | agent that auto-pays 402s (pay_and_get) with a client-side spend limit |
router/eip3009.py | the one crypto-subtle file: EIP-3009 typed-data, shared by buyer+facilitator so they can't drift |
router/facilitator_mock.py | in-process verify+settle (real sig check, mock chain) — the dry-run rail |
router/facilitator_real.py | live x402 facilitator over HTTP via the x402 SDK's own client; get_facilitator() picks mock↔real by config |
router/config.py | network/asset facts + .env loader; mock↔testnet↔mainnet is a one-line env change |
run_demo.py | end-to-end smoke (ephemeral keys, mock facilitator) |
run_live.py | live runner — settles a real x402 payment on Base Sepolia |
Go live (Base Sepolia testnet)
-
Two testnet wallets (buyer signs, seller receives):
python3 -c "from eth_account import Account; a=Account.create(); print('addr', a.address); print('key', a.key.hex())"Do this twice. Keep the keys out of git (use
.env). -
Fund the buyer with Base Sepolia testnet USDC (Circle faucet) + a little testnet ETH for any gas the facilitator relays.
-
.env(copy.env.example→.env, it's gitignored + auto-loaded):APV0_NETWORK=base-sepolia APV0_BUYER_PRIVATE_KEY=0x... # buyer testnet key (signs) APV0_SELLER_ADDRESS=0x... # seller address (receives) APV0_FACILITATOR_URL=https://x402.org/facilitator -
Run it live:
python3 run_live.pyThe seller now uses
RealFacilitator(the x402 SDK's own facilitator client), the buyer auto-pays the 402, and x402.org broadcasts the EIP-3009 USDC transfer on-chain. You get a real tx hash →https://sepolia.basescan.org/tx/<hash>.Gasless: with EIP-3009 the facilitator relays gas, so the buyer only needs testnet USDC, not ETH.
Gate your own endpoint (the product primitive)
from router.paywall import Paywall
from router.facilitator_real import get_facilitator
paywall = Paywall(get_facilitator(), my_requirements_fn) # mock ↔ real by env
@app.get("/my-endpoint")
def my_endpoint(request: Request):
return paywall.gate(request, lambda: do_expensive_work())
That one .gate() call handles the whole x402 V2 dance — 402 challenge → verify →
settle → record receipt → deliver — and appends every settlement to the
receipt-ledger. The deployer never touches the protocol or holds a key.
v1 dogfood — pay an agent, get REAL work back
v0 proved the payment. v1 proves the loop: a buyer agent pays → a seller agent
does real inference → returns the result + a settlement receipt. The seller's
_do_the_work(task) is the product's integration point (plug in your own
model/compute/service).
APV0_OPENROUTER_KEY=sk-or-... python3 run_v1_dogfood.py "your task here"
→ V1 DOGFOOD PASS — agent paid agent for real work ✅ (mock payment + real model
call by default; set APV0_NETWORK=base-sepolia for a real on-chain settle under
the same loop). Without a key it returns a stub so the product still runs.
This is the authentic loop: an agent doing real work, metered + paid-for over x402 — the same primitive whether the work is a model call, a compute job, or any other billable agent task.