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

# Rerank documents by relevance

> Rank document strings against a query. Requires a model whose output_modality is rerank. Billed on provider-reported input tokens only; non-streaming. Input is capped at 1,200,000 characters across query/document pairs, including the repeated query and optional task.



## OpenAPI

````yaml /openapi.yaml post /v1/rerank
openapi: 3.1.0
info:
  title: Impossibl AI API
  version: 0.0.1
  description: >
    The Impossibl AI API is one API for all AI providers, OpenAI-compatible
    across OpenAI,

    Anthropic, Google, xAI, and more (`GET /v1/models` lists the full catalog),

    billed from a prepaid credit balance.


    Provider usage is billed at provider list prices with no usage markup.

    Prepaid credit purchases charge a separate fixed 5% platform fee before tax.


    **Agent quickstart**

    1. `POST /v1/accounts` — create a funded account; you get an API key and a
       signup-bonus balance in one call (no human step required).
    2. Call `POST /v1/chat/completions`, `POST /v1/responses`, or
       `POST /v1/audio/transcriptions` with
       `Authorization: Bearer <key>` and a `provider/model` id from `GET /v1/models`.
    3. Credits are deducted per request by token or audio-duration usage; check
    `GET /v1/account`.
servers:
  - url: https://api.impossibl.com
    description: Production
  - url: http://localhost:8787
    description: Local dev
security:
  - BearerKey: []
paths:
  /v1/rerank:
    post:
      summary: Rerank documents by relevance
      description: >-
        Rank document strings against a query. Requires a model whose
        output_modality is rerank. Billed on provider-reported input tokens
        only; non-streaming. Input is capped at 1,200,000 characters across
        query/document pairs, including the repeated query and optional task.
      operationId: rerankDocuments
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/RerankRequest'
      responses:
        '200':
          description: >-
            Documents ordered by descending relevance score, with their original
            zero-based indices.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RerankResponse'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '402':
          $ref: '#/components/responses/InsufficientCredits'
        '404':
          $ref: '#/components/responses/UnknownModel'
        '502':
          $ref: '#/components/responses/UpstreamError'
        '503':
          $ref: '#/components/responses/ProviderNotConfigured'
components:
  schemas:
    RerankRequest:
      type: object
      required:
        - model
        - query
        - documents
      properties:
        model:
          type: string
          example: qwen/qwen3-reranker-8b
        query:
          type: string
          minLength: 1
          description: Search query used to score each document.
        documents:
          type: array
          minItems: 1
          maxItems: 1000
          items:
            type: string
            minLength: 1
        top_n:
          type: integer
          minimum: 1
          description: >-
            Number of results, at most the document count; defaults to all
            documents.
        return_documents:
          type: boolean
          default: true
          description: Include original document text in each result.
        task:
          type: string
          minLength: 1
          description: Optional description of the ranking task.
    RerankResponse:
      type: object
      required:
        - object
        - model
        - data
        - usage
      properties:
        object:
          type: string
          enum:
            - list
        model:
          type: string
          example: qwen/qwen3-reranker-8b
        data:
          type: array
          items:
            type: object
            required:
              - index
              - relevance_score
            properties:
              index:
                type: integer
                minimum: 0
                description: Original zero-based document index.
              relevance_score:
                type: number
              document:
                type: string
                description: Original text
                present unless return_documents is false.: null
        usage:
          type: object
          required:
            - prompt_tokens
            - total_tokens
          properties:
            prompt_tokens:
              type: integer
              minimum: 1
            total_tokens:
              type: integer
              minimum: 1
    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            message:
              type: string
            type:
              type: string
              description: >-
                One of authentication_error, invalid_request_error,
                insufficient_quota, upstream_error, provider_not_configured.
  responses:
    BadRequest:
      description: Malformed request (bad JSON, or missing required fields).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: '`model` and `messages` are required'
              type: invalid_request_error
    Unauthorized:
      description: Missing or invalid API key.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: Invalid API key
              type: authentication_error
    InsufficientCredits:
      description: The account's credit balance is empty. Top up to continue.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: Insufficient credits. Top up to continue.
              type: insufficient_quota
    UnknownModel:
      description: The requested `model` id is not in the registry (see GET /v1/models).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: 'Unknown model: foo/bar'
              type: invalid_request_error
    UpstreamError:
      description: The upstream provider returned an error.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: 'permission-denied: ...'
              type: upstream_error
    ProviderNotConfigured:
      description: The provider for this model has no API key configured on the gateway.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              message: 'Provider not configured: missing OPENAI_API_KEY'
              type: provider_not_configured
  securitySchemes:
    BearerKey:
      type: http
      scheme: bearer
      description: Gateway API key (`imp-rt-...`) from POST /v1/accounts or /v1/keys.

````