> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sanfoundation.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Check remaining balance

> Return the calling key's remaining spendable balance in dollars. Free —
this call is never billed. Works at any balance, including zero (returns
`"0.00"`), so an agent can always check its remaining balance.




## OpenAPI

````yaml https://gateway.sanfoundation.com/openapi.yaml get /api/v1/balance
openapi: 3.1.0
info:
  title: SAN Foundation Gateway API
  version: 1.0.0
  description: |
    Public API for the SAN Foundation gateway. The same data is exposed
    through two interchangeable surfaces: `/api/v1/*` is authenticated
    with an `x-api-key` (`sk_…`) and billed in credits (per-call cost
    in `x-credits`); `/x402/v1/*` is paid per call in USDC over the
    [x402 protocol](https://x402.org) and requires no API key (per-call
    cost in `x-price-usd`).
servers:
  - url: https://gateway.sanfoundation.com
    description: Production
security: []
tags:
  - name: API Key
    description: |
      Operations under `/api/v1/*`. Authenticate with a SAN API key
      (`x-api-key` header) and pay with prepaid credits — see each
      operation's `x-credits` for the per-call cost.
  - name: x402
    description: |
      Operations under `/x402/v1/*`. Pay per call in USDC over the
      [x402 protocol](https://x402.org) — see each operation's
      `x-price-usd` for the per-call cost. No API key required.
  - name: Registration
    description: |
      Public, unauthenticated self-onboarding for agents. One call mints an
      API key and grants the signup credit so an agent can immediately use
      `/api/v1/*`. Rate limited per client IP.
paths:
  /api/v1/balance:
    get:
      tags:
        - API Key
      summary: Check remaining balance
      description: |
        Return the calling key's remaining spendable balance in dollars. Free —
        this call is never billed. Works at any balance, including zero (returns
        `"0.00"`), so an agent can always check its remaining balance.
      operationId: getBalance
      responses:
        '200':
          $ref: '#/components/responses/BalanceOk'
        '401':
          $ref: '#/components/responses/Unauthorized'
      security:
        - ApiKeyAuth: []
components:
  responses:
    BalanceOk:
      description: OK — current spendable balance for the calling key.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/BalanceResponse'
    Unauthorized:
      description: >-
        Missing, invalid, or revoked API key (emitted by key-authenticated
        `/api/*` endpoints).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          examples:
            missing:
              value:
                error: Missing or invalid x-api-key header
            invalid:
              value:
                error: Invalid API key
  schemas:
    BalanceResponse:
      type: object
      required:
        - balance
      properties:
        balance:
          type: string
          description: >-
            Remaining spendable balance in dollars (e.g. "73.41"). "0.00" when
            empty.
    Error:
      type: object
      required:
        - error
      properties:
        error:
          type: string
        ref:
          type: string
          description: Echoed back when an agent ref could not be resolved.
        eventId:
          type: string
          description: Echoed back when an event id could not be resolved.
        min:
          type: integer
          description: Echoed back on a `limit out of range` error.
        max:
          type: integer
          description: Echoed back on a `limit out of range` error.
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: header
      name: x-api-key
      description: |
        SAN-issued API key (`sk_…`) issued from the SAN Agents Dashboard
        (Settings → API Keys). Used by every `/api/v1/*` endpoint; usage
        is billed in credits against the owning account's active Stripe
        subscription.

````