# Financial Comptroller — x402

> Agentic KG Holdings → https://agent-kg.ai. This surface implements the rail it is named after. Nothing here is endorsed by any protocol's owner. Prices are placeholders set by the office.

x402 is a payment protocol over HTTP: a resource that costs money answers 402 Payment Required with an offer, the client signs the payment and repeats the call, and the answer comes back with a settlement response. This surface implements x402 version 2 as the specification reads: the offer travels in the PAYMENT-REQUIRED header and body, the payment in PAYMENT-SIGNATURE, the settlement in PAYMENT-RESPONSE, all base64-encoded JSON.

## Doors

- https://agent-x402.ai/api — the paid door (x402 v2: 402 without payment, the office door's statement and a signed receipt with PAYMENT-SIGNATURE)
- https://agent-x402.ai/offers.json — the two offers (placeholder prices)
- https://agent-x402.ai/x402/receipt/{nonce} — resolve a receipt
- https://agent-x402.ai/x402/settled.json — this host's register, four-host total beside it
- https://agent-x402.ai/x402/jwks.json — receipt key (kid fc-x402-2026-09)
- https://agent-kg.ai/mcp — the office door (Model Context Protocol (MCP)) — the product

## Rails on every host

- x402 — live, USDC on Base mainnet
- Machine Payments Protocol (MPP) — challenge, credential, receipt as the spec reads; settles in test mode once the office's Stripe test keys are placed
- Universal Commerce Protocol (UCP) — /checkout-sessions REST; /.well-known/ucp published when a handler can settle
- Agentic Commerce Protocol (ACP) — /checkout_sessions at API-Version 2025-09-12; /acp/feed.jsonl served when the rail can settle

## The four

- https://agent-x402.ai/
- https://agent-mpp.ai/
- https://agent-ucp.ai/
- https://agent-acp.ai/

## Kit

- https://agent-x402.ai/.well-known/agent-card.json · https://agent-x402.ai/.well-known/jwks.json · https://agent-x402.ai/.well-known/mcp.json · https://agent-x402.ai/.well-known/ai-catalog.json · https://agent-x402.ai/.well-known/security.txt · https://agent-x402.ai/facts.json · https://agent-x402.ai/health.json · https://agent-x402.ai/index.md (Markdown twin, also on Accept: text/markdown)

Surface 0.1.0 · as of 2026-09-19. No cookies. No tracking.