Show HN: Tarfio bounded spending controls for MCP 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 and Threat Model 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, Deployment, and Backup/Restore Drill.

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 <spend-token> and X-MCPay-Nonce: <nonce>. The gateway removes both headers before forwarding upstream.

The control-plane gateway configuration supplies verification_keys. For a standalone gateway without --control-plane-api, pass --verification-keys "$MCPAY_VERIFICATION_KEYS".

The JavaScript and Python SDKs are not published to npm or PyPI as of September 8, 2026. Install them from this repository only.

npm install
npm run build --workspace=@mcpay/sdk-js

Workspace code can then import @mcpay/sdk-js. For use from another local Node project, install the repository path after building:

npm install ../Tarfio/packages/sdk-js

Install the Python SDK in editable mode from the repository root:

python -m pip install -e ./packages/sdk-python

See JavaScript SDK and Python SDK. Direct SDK wrappers use volatile process state in development; the persistent gateway is the supported beta path for crash recovery.

go test ./...
go test -race ./...
go vet ./...
go build ./cmd/...
npm ci
npm run build
npm run test
python -m pip install build
python -m build packages/sdk-python
python -m unittest discover -s packages/sdk-python/tests

PostgreSQL tests require a disposable migrated database in MCPAY_TEST_DATABASE_URL. They truncate application tables; never point them at retained data.

Tarfio is source-available under the Business Source License 1.1. BSL 1.1 is not an OSI-approved open-source license. The Additional Use Grant and change date are defined in LICENSE. The dashboard has a separate MIT license and upstream attribution in apps/dashboard/LICENSE.