Show HN: Tarfio bounded spending controls for MCP tools Tarfio, a private beta service announced on September 8, 2026, introduces bounded spending controls for MCP tools, enabling AI-agent teams to set hard limits on test-credit budgets, maximum price per call, allowed tools, expiry, and revocation. The service, which does not yet enable live payments or creator payouts, allows MCP creators to set test-credit prices per successful tool call without embedding billing logic, and includes features such as signed spend sessions, outcome receipts, replay protection, and idempotent processing. Tarfio is in development for a hosted beta with planned monthly subscription plans for selected tools. Give AI agents a budget, not your credit card. Hard spending limits for MCP tools and test-credit pricing for successful tool calls. Private beta with test credits. Live payments and creator payouts are not enabled. Tarfio gives AI-agent teams bounded access to MCP tools. A spend session can limit the total test-credit budget, maximum price per call, allowed tools, expiry, and revocation. MCP creators can set a test-credit price for each successful tool action without putting billing logic inside every tool handler. Tarfio records outcomes and receipts and protects covered paths from duplicate processing. - Set a test-credit price per successful tool call. - Keep your MCP at its own URL and behind its own gateway. - Give agent teams a clear outcome and receipt for each logical call. - Prepare monthly plans for selected tools before the hosted beta opens. - Set a total test-credit budget for an agent session. - Limit the maximum price of one tool call. - Choose which tools the agent may use. - Set an expiry and revoke access when needed. - Review outcomes and receipts without counting covered retries twice. Status as of September 8, 2026: private beta with test credits. Live payments, cards, and creator payouts are not enabled. Tarfio currently covers: - test-credit pricing per successful tool call; - creator-defined tool prices; - signed bounded spend sessions; - total budgets and maximum price per call; - allowed-tool restrictions, expiry, and revocation; - outcomes and receipts; - replay protection and idempotent processing for covered paths; - catalog and discovery; - a Go API, gateway, worker, PostgreSQL migrations, dashboard, and local SDK source. Hosted access is not open yet. The current beta does not accept, hold, transfer, or pay out real funds. Status: In development for the hosted beta. The planned monthly mode lets an MCP creator publish a versioned plan for one MCP server and selected tools. A plan has a monthly price in test credits and an included number of successful calls. The subscription design uses UTC billing periods, reserves allowance before a tool call, consumes allowance only for eligible successful outcomes, and stops calls when the included allowance reaches zero. Overage billing and silent fallback to per-call billing are not planned for this beta. flowchart LR Agent AI Agent API Tarfio API Gateway Tarfio Gateway Database PostgreSQL Tool MCP Tool Worker Usage Worker Agent -- |Create bounded spend session| API API -- |Reserve test credits| Database API -- |Return signed spend token| Agent Agent -- |tools/call with token and nonce| Gateway Gateway -- |Claim logical call| Database Gateway -- |Forward request| Tool Tool -- |Return outcome| Gateway Gateway -- |Deliver outcome| Agent Gateway -.- |Upload usage batch| API API -.- |Store idempotent usage| Database Worker -- |Apply test-credit ledger entries| Database classDef primary fill: 111827,color: ffffff,stroke: 111827,stroke-width:2px classDef service fill: f8fafc,color: 111827,stroke: 94a3b8,stroke-width:1.5px classDef storage fill: ecfccb,color: 111827,stroke: 65a30d,stroke-width:1.5px class Agent,API,Gateway primary class Tool,Worker service class Database storage The gateway records dispatch before contacting the upstream tool. If a process or network failure happens after dispatch, the tool may have executed even if the caller receives an error. For eligible successful outcomes, durable usage preparation happens before response delivery. Tarfio does not claim exactly-once tool delivery or exactly-once charging. The beta rejects metered 2xx text/event-stream responses before forwarding upstream success headers or body bytes and records no usage for them. Unmetered MCP traffic can still stream through the gateway. Spend tokens contain readable claims protected by Ed25519 signatures. They are not encrypted. The API holds the active signing private key; gateways receive a public verification keyring and select keys by the protected JWT kid header. The beta also uses: - HttpOnly , SameSite=Strict browser cookies; - bcrypt password hashes; - hashed invite and session tokens in PostgreSQL; - server-scoped, versioned gateway credentials; - HTTPS outside explicit local-development mode; - integer minor units and database transactions; - redirect blocking, header stripping, and request size and time limits in the gateway. Database rows are not encrypted by the application. Protect PostgreSQL storage, backups, signing keys, gateway secrets, and deployment environment files with operator-controlled encryption and access controls. Read Security Policy /yiaany/Tarfio/blob/main/SECURITY.md and Threat Model /yiaany/Tarfio/blob/main/docs/threat-model.md before exposing a deployment. Requirements: Docker Engine with Compose v2, Go 1.25+, and 4 GB of available memory. cp deploy/.env.beta.example deploy/.env.beta go run ./cmd/mcpay-keygen --key-id beta-2026-08 Put the generated keys in deploy/.env.beta , replace every replace- value, and start the stack: docker compose --env-file deploy/.env.beta -f deploy/compose.beta.yml config docker compose --env-file deploy/.env.beta -f deploy/compose.beta.yml build docker compose --env-file deploy/.env.beta -f deploy/compose.beta.yml up -d docker compose --env-file deploy/.env.beta -f deploy/compose.beta.yml ps Open http://localhost:8080 . Any top-up is a test credit with no cash value. Verify the stack: MCPAY BETA URL=http://localhost:8080 ./scripts/verify-central-beta.sh ./scripts/verify-central-beta.ps1 -BaseUrl http://localhost:8080 See Central Beta Runbook /yiaany/Tarfio/blob/main/docs/central-beta-runbook.md , Deployment /yiaany/Tarfio/blob/main/docs/beta-deployment.md , and Backup/Restore Drill /yiaany/Tarfio/blob/main/docs/backup-restore-drill.md . Create a server and action in the dashboard, issue a server-scoped gateway credential, and run the gateway beside the MCP server. Use persistent local storage for --state-file and do not share one state file between processes. go run ./cmd/mcpay-gateway \ --target https://your-mcp-server.example \ --mcp-path /mcp \ --server-id srv example \ --environment beta \ --token-issuer mcpay.beta \ --control-plane-api https://api.example/v1/gateway/servers/srv example \ --nonce-claim-api https://api.example/v1/gateway/nonces/claim \ --usage-api https://api.example/v1/usage-records \ --usage-api-token "$MCPAY GATEWAY API TOKEN" \ --state-file ./mcpay-gateway.db Metered requests in the test-credit beta carry Authorization: Bearer