> ## Documentation Index > Fetch the complete documentation index at: https://docs.sailresearch.com/llms.txt > Use this file to discover all available pages before exploring further. # Get the custom domain target > Returns the hostname to point your DNS at before registering a custom domain. It is the same for every domain in your organization, so read it once and reuse it. Registering a hostname needs its DNS to resolve to this target already, so this is the first call to make. ## OpenAPI ````yaml /sailbox-openapi.json get /custom-domains openapi: 3.1.0 info: title: Sail Sailbox API version: '2026-07-26' description: >- Create and operate Sailboxes over HTTP. Sailboxes are fast-booting virtual machines that you can pause, resume, checkpoint, and fork. Three things need an SDK or the CLI: running commands and moving files, turning on SSH, and building an image. Once SSH is on you can use `ssh` and `scp` for the first of those. See the [HTTP API guide](/sailboxes-http-api). servers: - url: https://sailbox-api.sailresearch.com/v1 security: - BearerAuth: [] tags: - name: Apps description: Groups that own Sailboxes. One app per workload. - name: Lifecycle description: >- A Sailbox's whole life: create it, watch it, stop and start it, terminate it. - name: Checkpoints description: Save a Sailbox to start from later, and copy a running one. - name: Networking description: >- Publish ports, serve them on hostnames you own, and identify a Sailbox to other Sailboxes. - name: Volumes description: >- Shared storage that outlives any one Sailbox. Alpha: these endpoints can still change. - name: SSH access description: Certificates for connecting to a Sailbox with `ssh`. - name: Usage description: Resource usage and spend. - name: Identity description: Who your API key belongs to. paths: /custom-domains: get: tags: - Networking summary: Get the custom domain target description: >- Returns the hostname to point your DNS at before registering a custom domain. It is the same for every domain in your organization, so read it once and reuse it. Registering a hostname needs its DNS to resolve to this target already, so this is the first call to make. operationId: getCustomDomainDNSConfig responses: '200': description: The target for your organization. content: application/json: schema: $ref: '#/components/schemas/CustomDomainDNSConfig' example: cname_target: 1a2b3c4d5e6f7890.sailboxes.sailresearch.com '401': description: The API key is missing or invalid. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: Invalid API key type: authentication_error param: null code: invalid_api_key '402': description: >- The organization is out of credits. The error carries a `billing_url` pointing at the page where you add them. Retry once you have. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: >- Your API key has been disabled due to insufficient credits. Visit https://app.sailresearch.com/billing to add credits. type: billing_error param: null code: credits_exhausted billing_url: https://app.sailresearch.com/billing '403': description: >- The API key is not allowed to perform this operation, or it is not scoped to an organization, which a custom domain target belongs to. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: sailboxes require an organization-scoped API key type: permission_error param: null code: null '429': description: >- For its first ten minutes a new organization is capped on how many requests it can have in flight at once, and yours is over that cap. The request never started, so retry it unchanged after the delay in the `Retry-After` header. The limit clears as those requests finish. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: >- Too many concurrent requests. Please retry after some of your organization's in-flight requests complete. type: rate_limit_error param: null code: rate_limited headers: Retry-After: $ref: '#/components/headers/RetryAfter' '500': description: Server error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: failed to fetch sailbox type: server_error param: null code: null '503': description: >- Sail is momentarily unavailable. Retry after the delay in the `Retry-After` header when one is present, and with backoff otherwise. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: Authentication service unavailable type: server_error param: null code: null headers: Retry-After: $ref: '#/components/headers/RetryAfter' components: schemas: CustomDomainDNSConfig: type: object required: - cname_target properties: cname_target: type: string description: >- Hostname to point your DNS at with a CNAME record. It is the same for every domain in your organization, so you can read it once and reuse it. ErrorResponse: type: object required: - error properties: error: $ref: '#/components/schemas/ErrorObject' ErrorObject: type: object required: - message - type - param - code properties: message: type: string description: Human-readable description of what went wrong. type: type: string description: >- Error category: `invalid_request_error`, `authentication_error`, `permission_error`, `billing_error`, `not_found_error`, `conflict_error`, `rate_limit_error`, or `server_error`. param: oneOf: - type: string - type: 'null' description: >- The request field the error refers to, when the error is about one field. code: oneOf: - type: string - type: integer - type: 'null' description: Stable short code for the error, when one applies. billing_url: type: string format: uri description: Page where you add credits. Sent with a 402. additionalProperties: true headers: RetryAfter: description: >- How many seconds to wait before retrying. On a 429 it also means the request never started, so the retry can reuse the same `Idempotency-Key`. schema: type: integer minimum: 0 securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: API Key ````