mails-ai Billing API

openapi: 3.2.0
info:
  title: Mails.ai Billing API
  version: 0.2.0
  description: 'The Mails.ai API gives AI agents a real email identity: send and receive

    transactional email. Mail received within your plan''s limits is scanned for prompt injection and

    reaches you as a typed event. With classification turned on (a paid-plan feature), new mail can also

    be read for intent; a reply in a thread never is.


    ## Authentication

    All endpoints take a Bearer API key:


    ```

    Authorization: Bearer mk_live_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

    ```


    Keys carry one or more scopes — `send`, `read`, `draft` (writes drafts, but can neither send nor

    schedule one) and `manage` — and a mode: **live** (`mk_live_…`) or **test** (`mk_test_…`).


    ## Test mode

    A `mk_test_` key exercises the entire API — real validation, persisted resources, real

    `message.sent`/`*.received` events and webhooks — without sending real email or incurring cost. Build and

    test your whole integration on a test key, then flip one character to `mk_live_` to go live.

    `POST /v1/test/inbound` (test key only) lets you simulate inbound mail end-to-end.


    ## Idempotency

    Send endpoints accept an `Idempotency-Key` header; a repeated key replays the stored response instead of

    sending twice, with an `Idempotent-Replay: true` header.


    ## Pagination

    List endpoints are cursor-paginated: pass `limit` (1–100) and the `next_cursor` from the previous page.


    ## Errors

    Errors use a stable envelope: `{ "error": { "type", "code", "message", "param", "request_id" } }`. Every

    response carries an `X-Request-Id` header for support correlation.'
  contact:
    name: Mails.ai Support
    url: https://mails.ai
    email: support@mails.ai
  license:
    name: Proprietary
    identifier: LicenseRef-Proprietary
servers:
- url: https://api.mails.ai
  description: Production
security:
- bearerAuth: []
tags:
- name: Billing
  description: Usage metering and the Stripe billing portal.
paths:
  /v1/billing/usage:
    get:
      tags:
      - Billing
      summary: Get current usage
      operationId: getBillingUsage
      description: '**Requires scope:** `read`. Returns metered usage for the current billing period plus the workspace''s tier caps. A key tied to one agent cannot read it (403 `insufficient_scope`): usage and costs are counted for the whole workspace, and `GET /v1/metrics` counts that agent''s mail.'
      responses:
        '200':
          description: Current-period usage and caps.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/BillingUsage'
        '401':
          description: Missing or invalid API key.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '403':
          description: The API key lacks the required scope (`insufficient_scope`), or the token belongs to an app connected by sign-in and this operation is closed to connected apps (`connected_app_not_allowed`).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '404':
          description: Resource not found in this workspace, or the agent a send names is archived (`agent_archived`).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '500':
          description: Internal server error.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
      x-required-scope: read
  /v1/billing/portal:
    post:
      tags:
      - Billing
      summary: Open billing portal or checkout
      operationId: openBillingPortal
      description: '**Requires scope:** `manage`. Returns a Stripe Billing Portal URL when already subscribed, otherwise a Checkout URL to subscribe. A workspace on an active paid plan with no Stripe subscription on file gets 409 `billing_state_inconsistent` instead of a Checkout URL, since subscribing again would bill it twice: contact support@mails.ai. Closed to apps connected by sign-in (403 `connected_app_not_allowed`): use the dashboard, an API key or the mails CLI.'
      requestBody:
        required: false
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/BillingPortalRequest'
            example:
              return_url: https://app.acme.com/settings/billing
      responses:
        '201':
          description: A redirect URL.
          content:
            application/json:
              schema:
                type: object
                properties:
                  url:
                    type: string
                    format: uri
                    description: 'The page to open: a Stripe Billing Portal session when the workspace has a subscription, otherwise a Stripe Checkout session for `price_lookup_key`. Both lead back to `return_url`. When `mock` is true, it is `return_url` itself with mock query parameters.'
                  mock:
                    type: boolean
                    description: True when the server runs with Stripe mocked, so no Stripe session was created; false for a real session.
                required:
                - url
        '400':
          description: Invalid request — malformed JSON or a field failed validation. Also `feature_not_enabled` when this server has a feature switched off (custom domains before they are available).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '401':
          description: Missing or invalid API key.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '403':
          description: The API key lacks the required scope (`insufficient_scope`), or the token belongs to an app connected by sign-in and this operation is closed to connected apps (`connected_app_not_allowed`).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '404':
          description: Resource not found in this workspace, or the agent a send names is archived (`agent_archived`).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '409':
          description: 'Conflict — duplicate resource, an in-progress idempotent request, a draft or scheduled message that started sending while it was being changed, or a thread deleted for good while one of its messages is being sent (`duplicate_resource`); or an agent name more than one agent has (`agent_name_conflict`: use the agent''s id); or a status change on an archived agent, since archiving cannot be undone (`agent_archived`).'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '500':
          description: Internal server error.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
      x-required-scope: manage
components:
  schemas:
    BillingUsage:
      type: object
      properties:
        workspace_id:
          type: string
          description: Your workspace id (`wsk_…`).
        tier:
          type: string
          description: 'Your plan: `free`, `pro`, `scale` or `metered`, or an older plan, `outbound` or `outbound_pro`. While a payment is past due, `caps` are Free''s whatever this says.'
        tier_status:
          type: string
          description: '`active`, or `past_due` after a failed renewal payment: the workspace then has Free plan limits until the payment goes through. `canceled` and `paused` refuse every send, with 402 `subscription_canceled` and `payment_required`.'
        period_start:
          type: string
          format: date-time
          description: 'Start of the usage period: the first day of this month, 00:00 UTC. The counts in `usage` start over each month.'
        period_end:
          type: string
          format: date-time
          description: 'End of the usage period, exclusive: the first day of next month, 00:00 UTC.'
        usage:
          type: object
          properties:
            sends:
              type: integer
              description: 'Recipients sent to this period: each live message counts once per `to`, `cc` and `bcc` address, and test sends do not count. `caps.monthly_sends` limits it.'
            parses:
              type: integer
              description: Received emails processed this period, which `caps.monthly_parses` limits. Mail kept or dropped over a limit counts in `inbound_skipped` instead.
            inbound_skipped:
              type: integer
              description: 'Received emails not processed this period: kept unclassified because the monthly allowance was used up or the subscription is inactive, or dropped unstored in a flood past `hourly_inbound` or `daily_inbound`.'
            webhook_deliveries:
              type: integer
              description: Webhook deliveries your endpoints accepted with a 2xx answer this period. Test deliveries are not counted.
            sends_cost_usd:
              type: number
              description: Estimated cost of delivering this period's sends, at $0.0001 per recipient. It is not what your plan charges.
            parses_cost_usd:
              type: number
              description: Estimated cost of classifying this period's received mail. Like `sends_cost_usd`, it is not what your plan charges.
          required:
          - sends
          - parses
          - webhook_deliveries
          description: This period's counts.
        caps:
          type: object
          properties:
            monthly_sends:
              type:
              - integer
              - 'null'
              description: Recipients the workspace may send to in a month, each live message counted once per `to`, `cc` and `bcc` address; past it, a send gets 429 `monthly_limit_exceeded` (`free_tier_exceeded` on Free limits). Null when the plan has no monthly limit.
            monthly_parses:
              type:
              - integer
              - 'null'
              description: Received emails processed in a month; past it, mail is still stored but not classified, and counts in `inbound_skipped`. Null when the plan has no monthly limit.
            agents:
              oneOf:
              - type: integer
              - type: string
                enum:
                - unlimited
              description: How many agents the plan allows, or the string `unlimited`. Past it, `POST /v1/agents` gets 402 `resource_cap_exceeded`.
            hourly:
              type: integer
              description: 'Recipients the workspace may send to in any rolling hour, counted like `monthly_sends`: once per `to`, `cc` and `bcc` address. Mail scheduled for later counts from when it was accepted; mail that was canceled or refused does not count. Past it, a send gets 429 `hourly_limit_exceeded`. Test sends do not count.'
            daily:
              type: integer
              description: Recipients the workspace may send to in any rolling 24 hours, counted as `hourly` is. Past it, a send gets 429 `daily_limit_exceeded`. Test sends do not count.
            hourly_inbound:
              type: integer
              description: Received emails stored in any rolling hour. Past it, more mail is dropped without being stored, and counts in `inbound_skipped`.
            daily_inbound:
              type: integer
              description: Received emails stored in any rolling 24 hours. Past it, more mail is dropped without being stored, and counts in `inbound_skipped`.
          required:
          - monthly_sends
          - monthly_parses
          - agents
          description: 'The limits of the plan the workspace is held to now: its own, or Free''s while a payment is past due.'
      required:
      - workspace_id
      - tier
      - usage
      - caps
    BillingPortalRequest:
      type: object
      properties:
        return_url:
          type: string
          format: uri
          description: 'Where the customer lands after leaving the billing portal, or after finishing or cancelling checkout: an absolute URL. Left out, it is the dashboard''s `/billing` page.'
        price_lookup_key:
          type: string
          minLength: 1
          maxLength: 64
          description: 'The plan checkout subscribes to: `mailsai_pro_monthly` (the default), `mailsai_scale_monthly`, `mailsai_pro_yearly` or `mailsai_scale_yearly`. Used only when the workspace has no subscription yet; any other value is a 400 `invalid_param_value`.'
      additionalProperties: false
    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            type:
              type: string
              enum:
              - invalid_request_error
              - authentication_error
              - permission_error
              - rate_limit_error
              - resource_error
              - payment_error
              - abuse_error
              - api_error
              description: High-level error category.
            code:
              type: string
              enum:
              - invalid_field
              - missing_field
              - missing_param
              - invalid_param_value
              - method_not_allowed
              - invalid_idempotency_key
              - duplicate_resource
              - slug_invalid
              - slug_reserved
              - slug_taken
              - agent_name_conflict
              - body_too_large
              - missing_authorization
              - missing_api_key
              - invalid_api_key
              - expired_api_key
              - revoked_api_key
              - invalid_access_token
              - email_not_verified
              - insufficient_scope
              - connected_app_not_allowed
              - sso_required
              - workspace_mismatch
              - agent_not_owned
              - rate_limit_exceeded
              - daily_limit_exceeded
              - hourly_limit_exceeded
              - monthly_limit_exceeded
              - agent_not_found
              - agent_paused
              - agent_archived
              - resource_not_found
              - recipient_suppressed
              - recipient_not_allowed
              - domain_not_verified
              - ses_role_not_assumable
              - ses_role_external_id_not_required
              - ses_permission_denied
              - ses_setup_failed
              - ses_message_rejected
              - ses_events_not_confirmed
              - payment_required
              - payment_method_failed
              - subscription_canceled
              - billing_state_inconsistent
              - free_tier_exceeded
              - plan_limit_exceeded
              - cold_email_prohibited
              - agent_suspended
              - new_workspace_fanout_exceeded
              - resource_cap_exceeded
              - workspace_cap_exceeded
              - feature_not_enabled
              - test_mode_required
              - live_mode_required
              - unknown_test_address
              - workspace_not_approved
              - spam_pattern_detected
              - classifier_rejected
              - high_injection_score
              - complaint_threshold_exceeded
              - bounce_threshold_exceeded
              - internal_error
              - internal_server_error
              - upstream_error
              - upstream_unavailable
              - service_unavailable
              description: Stable machine-readable error code.
            message:
              type: string
              description: Human-readable explanation.
            param:
              type:
              - string
              - 'null'
              description: The offending request field, when applicable.
            request_id:
              type: string
              description: Echo of the X-Request-Id header for support correlation.
            errors:
              type: array
              items:
                $ref: '#/components/schemas/FieldError'
              description: On a validation failure, EVERY offending field (not just the first). The top-level code/message/param mirror errors[0] for backward compatibility.
            resets_at:
              type:
              - string
              - 'null'
              format: date-time
              description: 'On every 429: when the limit lets the request through again (UTC). Null when waiting will not help, for a cap that only an upgrade or a deletion lifts.'
            retry_after_seconds:
              type:
              - integer
              - 'null'
              description: 'On every 429: the seconds until `resets_at`, null when it is null. On any other error that says how long to wait, such as a 503 `upstream_unavailable`: the seconds its `Retry-After` header gives.'
            upgrade_url:
              type: string
              format: uri
              description: 'On every 402: the dashboard page where the plan can be changed, `https://app.mails.ai/billing`.'
          required:
          - type
          - code
          - message
          description: 'The error, as every error response carries it: `type`, `code`, `message`, `param` and `request_id`, plus `errors` on a validation failure, `resets_at` and `retry_after_seconds` on a 429, `retry_after_seconds` on any other error with a `Retry-After`, and `upgrade_url` on a 402. A failed item in a batch send is the same error, and `retry_after_seconds` is how it says how long to wait, since an item has no headers of its own.'
      required:
      - error
    FieldError:
      type: object
      properties:
        code:
          type: string
          enum:
          - invalid_field
          - missing_field
          - missing_param
          - invalid_param_value
          - method_not_allowed
          - invalid_idempotency_key
          - duplicate_resource
          - slug_invalid
          - slug_reserved
          - slug_taken
          - agent_name_conflict
          - body_too_large
          - missing_authorization
          - missing_api_key
          - invalid_api_key
          - expired_api_key
          - revoked_api_key
          - invalid_access_token
          - email_not_verified
          - insufficient_scope
          - connected_app_not_allowed
          - sso_required
          - workspace_mismatch
          - agent_not_owned
          - rate_limit_exceeded
          - daily_limit_exceeded
          - hourly_limit_exceeded
          - monthly_limit_exceeded
          - agent_not_found
          - agent_paused
          - agent_archived
          - resource_not_found
          - recipient_suppressed
          - recipient_not_allowed
          - domain_not_verified
          - ses_role_not_assumable
          - ses_role_external_id_not_required
          - ses_permission_denied
          - ses_setup_failed
          - ses_message_rejected
          - ses_events_not_confirmed
          - payment_required
          - payment_method_failed
          - subscription_canceled
          - billing_state_inconsistent
          - free_tier_exceeded
          - plan_limit_exceeded
          - cold_email_prohibited
          - agent_suspended
          - new_workspace_fanout_exceeded
          - resource_cap_exceeded
          - workspace_cap_exceeded
          - feature_not_enabled
          - test_mode_required
          - live_mode_required
          - unknown_test_address
          - workspace_not_approved
          - spam_pattern_detected
          - classifier_rejected
          - high_injection_score
          - complaint_threshold_exceeded
          - bounce_threshold_exceeded
          - internal_error
          - internal_server_error
          - upstream_error
          - upstream_unavailable
          - service_unavailable
          description: Stable machine-readable code for this field.
        message:
          type: string
          description: Human-readable explanation for this field.
        param:
          type:
          - string
          - 'null'
          description: The offending request field (dot-path), or null.
      required:
      - code
      - message
      - param
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: mk_live_<32 hex>, mk_test_<32 hex>, or moa_<48 hex>
      description: 'A Mails.ai API key, or an OAuth access token (`moa_…`, valid for 1 hour) from signing in through an app such as the CLI, Claude or ChatGPT. OAuth discovery: https://api.mails.ai/.well-known/oauth-authorization-server and https://api.mails.ai/.well-known/oauth-protected-resource. An access token''s OAuth scope maps onto these API scopes: `full_access` = `send` + `read` + `manage` (not `draft`: the draft routes take those three too), `send` = `send` + `read`, `read` = `read`. Scopes (`send`/`read`/`manage`/`draft`) are noted per operation via `x-required-scope`; when more than one scope opens an operation (the draft routes also take `draft`), `x-accepted-scopes` lists them all. `inbox` appears there too, on the triage routes (changing and trashing threads, labels, cancelling a scheduled send): only a signed-in dashboard session holds it (a workspace Member''s), never an API key or OAuth token, and `x-session-scopes` names it.'