Signal Registration API

openapi: 3.1.0
info:
  title: Signal Server Accounts Registration API
  description: The Signal Server API is the backend REST API that supports the Signal Private Messenger applications on Android, Desktop, and iOS. Built as a Dropwizard application, it provides REST controllers for account registration and management, message delivery, pre-key bundle distribution, device provisioning, profile management, and attachment handling. The server handles user registration via phone number verification, encrypted message routing, push notification delivery, and pre-key bundle management. While Signal does not offer an official public REST API for third-party use, the server source code is available for inspection and self-hosting. All communication is end-to-end encrypted using the Signal Protocol.
  version: '2.0'
  contact:
    name: Signal Support
    url: https://support.signal.org/
  termsOfService: https://signal.org/legal/
  license:
    name: AGPL-3.0
    url: https://github.com/signalapp/Signal-Server/blob/main/LICENSE
servers:
- url: https://chat.signal.org
  description: Signal Production Server
security:
- basicAuth: []
tags:
- name: Registration
  description: Account registration endpoints for creating new Signal accounts via phone number verification.
paths:
  /v1/registration:
    post:
      operationId: registerAccount
      summary: Register a new account
      description: Registers a new Signal account with a phone number. Initiates the verification process by sending an SMS or voice call with a verification code to the provided phone number.
      tags:
      - Registration
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/RegistrationRequest'
      responses:
        '200':
          description: Registration initiated successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RegistrationResponse'
        '400':
          description: Invalid request parameters
        '409':
          description: Account already exists or number is rate-limited
        '429':
          description: Rate limit exceeded
components:
  schemas:
    AccountAttributes:
      type: object
      properties:
        fetchesMessages:
          type: boolean
          description: Whether the device fetches messages via WebSocket rather than receiving push notifications.
        registrationId:
          type: integer
          description: The Signal Protocol registration ID for this device.
        pniRegistrationId:
          type: integer
          description: The PNI registration ID for this device.
        name:
          type: string
          description: The encrypted device name, Base64-encoded.
        capabilities:
          type: object
          description: Account capability flags indicating supported features.
          properties:
            storage:
              type: boolean
              description: Whether the account supports secure value recovery and storage service.
            transfer:
              type: boolean
              description: Whether the device supports account transfer.
            paymentActivation:
              type: boolean
              description: Whether the account supports payment activation.
        unidentifiedAccessKey:
          type: string
          description: The Base64-encoded unidentified access key for sealed sender.
        unrestrictedUnidentifiedAccess:
          type: boolean
          description: Whether any sender can use sealed sender without the access key.
    RegistrationRequest:
      type: object
      required:
      - sessionId
      - accountAttributes
      properties:
        sessionId:
          type: string
          description: The verification session identifier obtained from the registration service.
        accountAttributes:
          $ref: '#/components/schemas/AccountAttributes'
        skipDeviceTransfer:
          type: boolean
          description: Whether to skip the device transfer flow for existing accounts.
    RegistrationResponse:
      type: object
      properties:
        uuid:
          type: string
          format: uuid
          description: The UUID assigned to the newly registered account.
        number:
          type: string
          description: The E164-formatted phone number associated with the account.
        pni:
          type: string
          format: uuid
          description: The Phone Number Identity UUID for the account.
        storageCapable:
          type: boolean
          description: Whether the account supports secure storage service.
  securitySchemes:
    basicAuth:
      type: http
      scheme: basic
      description: HTTP Basic authentication using the account UUID (or phone number) and password. The password is established during account registration.
    bearerAuth:
      type: http
      scheme: bearer
      description: Bearer token authentication used for certain provisioning and registration flows.
externalDocs:
  description: Signal Server Source Code
  url: https://github.com/signalapp/Signal-Server