Payments & credits over MCP

Every MCP request is metered. Calls draw credits from the authenticated account's balance: a base protocol:call charge per request, with expensive tools (e.g. mail_send, search_web) priced higher — see the price book.

• Insufficient balance → HTTP 402 with requiredCredits/balanceCredits (and x402 payment requirements once crypto rails are enabled). Top up and retry.
• Spend cap reached → HTTP 403 with code: "spend_cap_reached".
• Charges are taken at admission; a call that fails scope/validation afterwards is still charged.

Two billing tools are available with the billing scope: credits_balance (balance, spend cap, prices) and credits_topup_crypto (deposit intent, when crypto rails are enabled). Human accounts can also manage credits at Settings → Credits.