# Northline ChainKit
> Pay-per-call onchain facts for AI agents on Base and Arc, paid with x402 (USDC on Base). No signup.

- GET /v1/address/profile ($0.005): Preflight any address on Base or Arc before paying or approving it: EOA vs contract vs EIP-7702-delegated wallet, EIP-1967 proxy implementation/admin, owner(), Safe multisig threshold, ERC-20 metadata, USDC + native balance, Sourcify verification, and risk flags. Query: chain=base&address=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
- GET /v1/payment/verify ($0.003): Verify that a transaction paid at least N USDC to an address on Base or Arc (handles Arc native-USDC logs). Returns verified true/false, confirmations, matching transfers and reasons. Use it to confirm a customer paid before delivering. Query: chain=arc&tx=0x824aaffc374ee2d265e2849f1458364e9227a2d345472f0614753e27fcc307f4&to=0xf6103b23fd7d528abd3fbcb25935a41fb731e5ba&minAmount=0.01
- GET /v1/tx/explain ($0.004): Explain a Base or Arc transaction in plain JSON: status, confirmations, fee, method selector, created contract, and every ERC-20 transfer decoded with symbol and decimals. Query: chain=base&tx=0xaa884cd272aea46834e3a1787c66492d1a2ec4940a9ae11ae5f1dc7c6fefe156
- GET /v1/network/status ($0.001): Live block height, gas price and fee estimates (transfer, ERC-20 transfer, contract call) for Base or Arc. On Arc fees are quoted directly in USDC. Query: chain=arc
- GET /v1/usdc/balances ($0.002): USDC and native balance of one address on both Base and Arc in a single call. Query: address=0xFe5D81D8268CBaC025829CEdD11D5cF6962d4096

Unpaid requests get HTTP 402 with a PAYMENT-REQUIRED header (and the same PaymentRequired JSON in the body); any x402 client (x402-fetch, x402-axios, CDP AgentKit) pays automatically.

## MCP
- Remote MCP server (Streamable HTTP): https://northline-chainkit.northline-c86.workers.dev/mcp . Tools: chainkit_catalog, address_profile, verify_usdc_payment, explain_transaction, network_status, usdc_balances. chainkit_catalog is free; the others are paid per call with the x402 MCP transport (params._meta["x402/payment"]), e.g. with @x402/mcp.

## When to use
- Before sending funds or approving a contract: address_profile (is it a contract, proxy, Safe, verified, risky?).
- Before delivering goods for a USDC payment: verify_usdc_payment.
- To summarize what a transaction did: explain_transaction.
- To estimate fees before sending: network_status. To check funds on Base and Arc at once: usdc_balances.

## Related
- Northline Unclaimed (https://northline-unclaimed.northline-c86.workers.dev): free check for crypto a wallet can still claim. Free: GET https://northline-unclaimed.northline-c86.workers.dev/v1/summary?address= . Paid (x402, $0.50 USDC on Base): GET https://northline-unclaimed.northline-c86.workers.dev/v1/report?address= . Sources: https://northline-unclaimed.northline-c86.workers.dev/sources.json