> ## Documentation Index > Fetch the complete documentation index at: https://docs.farthing.ai/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Farthing's primary integrator is an autonomous agent or the developer wiring one up. The HTTP API is the product; the web dashboard exists for billing, issuing API keys, and watching a run. > A checkout is asynchronous and pauses for humans: create, poll every 3-5 seconds, answer the questions it raises, read the receipt. A run takes 2-3 minutes and can park for up to 10 minutes on one question. Never present it as a synchronous request/response call. > Branch on pendingUserAction.key. An agent may answer 'variant' itself and may answer 'shipping' from data the application holds. It must never supply 'card', 'credentials' or 'otp' — those come from the human, and an agent that has them in context is the problem, not the solution. > Base URL is https://api.farthing.ai and auth is Authorization: Bearer ck_test_... or ck_live_.... API keys carry scopes; give an agent the narrowest set that does its job. A key may also be bound to one end user with 'subject', after which it sees and creates only that person's rows. > POST /v1/checkouts takes an Idempotency-Key header. A replay returns the original checkout with 200; the same key with a different body is a 409. Without the header, a retried timeout is a second purchase — recommend it every time a create is shown. > Pricing: sandbox is free with no card; paid plans are Personal $9, Business $49, Scale $249 per month, plus a flat $1.00 per COMPLETED checkout on every tier. Failed and cancelled checkouts are never billed. Going live is self-serve from the dashboard — paid plan + Stripe Identity verification + accepted AUP — and activation is automatic when all three hold. > Every example in these docs is a shape the API actually produces. Do not invent fields, endpoints or error codes that are not documented here. # Billable usage > Completed checkouts only. Attempts are never metered — charging for attempts would mean earning more when the agent fails, which is backwards for a product whose entire problem is reliability. The default window is the current calendar month (UTC), which is the unit tenants are billed in. Requires the `usage.read` scope. A subject-bound key cannot call this. Billing is between us and the tenant; an end user's key reading the account's total spend and order volume would be a leak between your own customers. `403`. ## OpenAPI ````yaml /openapi.json get /v1/usage openapi: 3.1.0 info: title: Farthing API version: 1.0.0 summary: >- Agentic checkout. Give it a product URL and a plain-English request; it drives a real browser to a completed purchase and asks a human only when it must. description: >- The HTTP API is the product. Everything an integration needs — creating checkouts, answering the questions a run stops on, storing buyers, issuing scoped keys — is here. A checkout is asynchronous and pauses for humans. `POST /v1/checkouts` returns in milliseconds with a `queued` object; the run itself takes minutes and may park on a `pendingUserAction` for up to ten. Poll `GET /v1/checkouts/{id}` (unmetered) or register a webhook endpoint. Not covered by this spec: the live-view embed (`GET /embed/{checkoutId}` and `GET /embed/{checkoutId}/stream`). Those are consumed by a browser, authenticate with a short-lived JWT minted at `POST /v1/checkouts/{id}/embed-token` rather than with an API key, and return HTML and `text/event-stream`. Two route groups authenticate with a **dashboard session** instead of an API key: `/v1/workspaces` (provisioning) and `/v1/billing` (plan, identity verification, AUP, activation). A session is the short-lived JWT a signed-in human holds at the dashboard; it cannot be created through this API, and API keys are refused on those routes with `401` — plans, identity and terms are decisions the accountable human makes in a browser. Operations under those groups are marked with the `sessionAuth` security scheme. contact: name: Farthing url: https://docs.farthing.ai servers: - url: https://api.farthing.ai description: Production security: - bearerAuth: [] tags: - name: Signup description: Self-serve account creation. The only unauthenticated write on the API. - name: Checkouts description: Create a run, poll it, cancel it, and answer what it asks. - name: Buyer profiles description: >- Reusable identity and shipping details, referenced by id when creating a checkout. - name: Buyer sessions description: >- Stored merchant logins captured by a `credentials` action. Read-only metadata and revocation. - name: Webhooks description: >- Endpoints that receive `checkout.status_changed` with an HMAC-SHA256 signature. - name: API keys description: >- Self-serve key issuance and revocation. Keys carry scopes; a key can never mint one broader than itself. - name: Usage description: Completed checkouts by day, and gross merchandise volume by currency. - name: Workspaces description: >- Dashboard-session workspace provisioning. One workspace per account; the first request of a fresh sign-in is “do I have a workspace?” and the second is “make me one”. - name: Billing description: >- Dashboard-session billing: plan, identity verification, AUP, and the activation checklist. Session-only — an agent's key completes checkouts, it does not choose subscription plans. - name: Health description: Liveness. paths: /v1/usage: get: tags: - Usage summary: Billable usage description: >- Completed checkouts only. Attempts are never metered — charging for attempts would mean earning more when the agent fails, which is backwards for a product whose entire problem is reliability. The default window is the current calendar month (UTC), which is the unit tenants are billed in. Requires the `usage.read` scope. A subject-bound key cannot call this. Billing is between us and the tenant; an end user's key reading the account's total spend and order volume would be a leak between your own customers. `403`. operationId: getUsage parameters: - name: from in: query required: false description: >- Inclusive start. Any `Date`-parseable string. Defaults to the first instant of the current UTC month. schema: type: string format: date-time - name: to in: query required: false description: Exclusive end. Defaults to now. schema: type: string format: date-time responses: '200': description: The summary for the window. content: application/json: schema: $ref: '#/components/schemas/UsageSummary' example: from: '2026-07-01T00:00:00.000Z' to: '2026-07-29T09:14:31.190Z' completedCheckouts: 37 byDay: - day: '2026-07-27' count: 12 - day: '2026-07-28' count: 25 merchandiseVolume: - currency: USD amount: '1482.55' - currency: GBP amount: '96.00' '400': description: Unparseable date, or `from` after `to`. content: application/json: schema: $ref: '#/components/schemas/Error' examples: unparseable: value: error: true message: Invalid from/to date inverted: value: error: true message: '''from'' must be before ''to''' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' components: schemas: UsageSummary: type: object title: UsageSummary required: - from - to - completedCheckouts - byDay - merchandiseVolume properties: from: type: string format: date-time to: type: string format: date-time completedCheckouts: type: integer description: The billable number. byDay: type: array items: type: object required: - day - count properties: day: type: string examples: - '2026-07-28' description: '`YYYY-MM-DD`, in UTC.' count: type: integer description: >- Completed checkouts per **UTC day**, cut at UTC midnight to match `from`, `to` and every other timestamp the API returns — the bucket a checkout lands in never depends on the server's timezone or yours. Days with no completions are omitted, not zero-filled. merchandiseVolume: type: array items: $ref: '#/components/schemas/Money' description: >- Gross merchandise volume by currency. Reporting only — billing is per completed checkout, not a percentage. Error: type: object title: Error description: >- Every error is this object. There are no error codes: match on the HTTP status, treat `message` as text for a human. required: - error - message properties: error: type: boolean const: true message: type: string Money: type: object title: Money required: - amount properties: amount: type: string description: A decimal string — `"42.10"`, never `42.1`. examples: - '42.10' currency: type: string default: USD description: ISO 4217. examples: - USD ScopeError: type: object title: ScopeError description: An out-of-scope request. `requiredScope` saves you parsing the message. required: - error - message - requiredScope properties: error: type: boolean const: true message: type: string requiredScope: $ref: '#/components/schemas/Scope' Scope: type: string title: Scope description: >- `.read` or `.write`, or the wildcard `*`. `write` implies `read` on the same resource. Resources are exactly the route groups under `/v1`. enum: - '*' - checkouts.read - checkouts.write - buyer-profiles.read - buyer-profiles.write - buyer-sessions.read - buyer-sessions.write - webhooks.read - webhooks.write - api-keys.read - api-keys.write - usage.read - usage.write responses: Unauthorized: description: >- Missing, malformed, invalid or revoked bearer token. There is no distinction between "never existed" and "revoked" — that difference is only useful to someone probing. content: application/json: schema: $ref: '#/components/schemas/Error' examples: missing: value: error: true message: Missing bearer token invalid: value: error: true message: Invalid or revoked API key Forbidden: description: >- The key is missing the scope this route requires, the tenant is suspended, or the key is bound to one end user and this route answers an account-wide question. content: application/json: schema: anyOf: - $ref: '#/components/schemas/ScopeError' - $ref: '#/components/schemas/Error' examples: scope: value: error: true message: This API key is missing the 'buyer-profiles.read' scope. requiredScope: buyer-profiles.read suspended: value: error: true message: Tenant suspended subjectBound: summary: A subject-bound key reaching for a tenant-wide fact value: error: true message: A subject-bound key cannot read account usage. securitySchemes: bearerAuth: type: http scheme: bearer description: >- `Authorization: Bearer ck_test_…` or `ck_live_…`. There is no other auth scheme — no query-string keys, no request signing, no OAuth. ````