> ## 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. # Tunnel to a port > Opens a WebSocket that carries one TCP connection from you to a port inside the Sailbox; nothing is published. Send the standard WebSocket upgrade headers on this GET. Binary messages carry bytes in either direction, the text message `{"type":"eof"}` half-closes the sender's direction, and a close frame ends the tunnel. The failure model, the close codes, the ping cadence, and the message limit are in [Connect to a port without publishing it](/sailboxes-http-api#connect-to-a-port-without-publishing-it). ## OpenAPI ````yaml /sailbox-openapi.json get /sailboxes/{sailbox_id}/tunnel openapi: 3.1.0 info: title: Sail Sailbox API version: '2026-09-07' description: >- Create and operate Sailboxes over HTTP. Sailboxes are fast-booting virtual machines that you can pause, resume, and checkpoint. Run commands, stream files, manage lifecycle and networking, and inspect usage. Turning on SSH and building an image still require an SDK or the CLI. 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: Exec description: Run commands and control their standard input and terminals. - name: Files description: Stream regular files into and out of a Sailbox. - name: Networking description: >- Publish ports, serve them on hostnames you own, and identify a Sailbox to other Sailboxes. - name: Secrets description: >- Organization values that HTTP policies can add to matching requests. Sail never returns a stored value. - name: HTTP policies description: Rules for HTTPS requests a Sailbox sends. - 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: /sailboxes/{sailbox_id}/tunnel: get: tags: - Networking summary: Tunnel to a port description: >- Opens a WebSocket that carries one TCP connection from you to a port inside the Sailbox; nothing is published. Send the standard WebSocket upgrade headers on this GET. Binary messages carry bytes in either direction, the text message `{"type":"eof"}` half-closes the sender's direction, and a close frame ends the tunnel. The failure model, the close codes, the ping cadence, and the message limit are in [Connect to a port without publishing it](/sailboxes-http-api#connect-to-a-port-without-publishing-it). operationId: tunnelSailboxPort parameters: - $ref: '#/components/parameters/SailboxId' - name: port in: query required: true schema: type: integer minimum: 1 maximum: 65535 description: >- Port a program inside the Sailbox listens on, at 127.0.0.1 or on all interfaces. responses: '101': description: The connection is now a WebSocket carrying the tunnel. '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '402': $ref: '#/components/responses/PaymentRequired' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/NotFound' '409': $ref: '#/components/responses/Conflict' '429': $ref: '#/components/responses/TooManyRequests' '500': $ref: '#/components/responses/ServerError' '503': $ref: '#/components/responses/TunnelUnavailable' '504': $ref: '#/components/responses/Timeout' components: parameters: SailboxId: name: sailbox_id in: path required: true schema: type: string description: >- Id of the Sailbox, as returned by create. It is `sb_` followed by a UUID. responses: BadRequest: description: The request was rejected. See the error message for the offending field. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: memory_limit_gib for size m must be between 8 and 128 type: invalid_request_error param: null code: null Unauthorized: 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 PaymentRequired: 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 Forbidden: description: The API key is not allowed to perform this operation. 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 NotFound: description: No Sailbox with that id exists in your organization. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: sailbox "sb_9c8f1e2a-3b4d-4f5a-8c7e-1d2f3a4b5c6d" not found type: not_found_error param: null code: null Conflict: description: The Sailbox is not in a state that allows this operation. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: sailbox listeners require persistence type: conflict_error param: null code: null TooManyRequests: description: >- Too many requests in flight, or the organization is at a limit. A `Retry-After` header means the request never started, so retry it unchanged after that delay. Without one, the request ran and hit the limit `message` names. Some of those clear on their own, such as a shortage of public ports; others need you to free something up first. Send the request again once the cause is gone. 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' ServerError: 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 TunnelUnavailable: description: >- Nothing is listening on the port inside the Sailbox, and `message` carries the connection error; or Sail is momentarily unavailable. Start the program, or retry with backoff. 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' Timeout: description: >- The operation outran its deadline, or a retry sent with the same `Idempotency-Key` waited about 30 seconds and the original request was still going. Retry with the same key. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: message: idempotent request still in flight type: server_error param: null code: null schemas: 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`, `quota_exceeded_error`, `not_implemented_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. Errors relayed from the Sailbox runtime carry its status token, for example `already_exists` or `failed_precondition` on a 409, which the HTTP status alone does not distinguish. 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 ````