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

# Get dataset schema

> Discover what field keys exist in each JSON bucket (inputs, expected_outputs, metadata, extras) across this dataset's items, along with a coverage count and inferred data type for each key. Useful for pre-populating a field mapper UI or for an MCP agent to understand what data is available before constructing a mapping. Returns empty objects for all buckets if the dataset has no items.



## OpenAPI

````yaml GET /v3/evals/datasets/{dataset_id}/schema
openapi: 3.0.3
info:
  title: Fiddler API - 2.0
  description: APIs to interact with Fiddler
  termsOfService: https://fiddler.ai/about/terms
  contact:
    email: support@fiddler.ai
  license:
    name: Proprietary
    url: '2.0'
  version: '2.0'
servers: []
security:
  - BearerAuth: []
tags:
  - name: access-key
    description: CRUD operations for API keys
  - name: span-v3
  - name: aggregation-invalidation-request-v3
    description: Endpoints related to retrieving aggregation invalidation requests
  - name: alert-rules-v3
    description: CRUD for Alert Rules, Summary, and Stats APIs
  - name: application-v3
  - name: attribute-v3
  - name: auth
    description: Authentication strategies and login flows
  - name: baseline-v3
    description: CRUD for baseline
  - name: catalog-v3
    description: >-
      Entity catalog provides paginated, searchable discovery of entity names
      (attribute keys, agent names, span types, span names) and their distinct
      values. Powered by ClickHouse materialized views — no worker or PostgreSQL
      dependency.
  - name: chart-annotation-v3
    description: Endpoints related to retrieving chart annotations
  - name: chart-v3
    description: CRUD for chart
  - name: queries-v3
    description: v3 queries API
  - name: configuration-v3
    description: CRUD for configurations
  - name: custom-metrics-v3
  - name: dimensionality-reduction-v3
  - name: environment-v3
    description: Endpoints related to environment management
  - name: evals
  - name: datasets
  - name: evaluation-v3
  - name: evaluator-v3
  - name: rule-evaluators-v3
  - name: experiment-v3
  - name: explainability-v3
  - name: llm_rca-v3
  - name: file-upload
    description: Endpoints related to file uploading.
  - name: fql-expressions-v3
    description: >
      Endpoints for listing FQL (Fiddler Query Language) functions available for
      GenAI custom metrics. Used by the frontend for autocomplete and signature
      hints in the FQL editor.
  - name: genai-alert-rules-v3
    description: CRUD API for GenAI Alert Rules
  - name: genai-custom-metrics-v3
    description: API for GenAI Custom Metrics
  - name: genai-metrics-v3
    description: >-
      Endpoints for pre-aggregated GenAI metrics. All metric data is
      pre-aggregated by an hourly ClickHouse refreshable materialized view; no
      real-time aggregation is performed at request time.
  - name: guardrails-api
    description: Endpoints related to retrieving Guardrails specific data
  - name: ingestion-v3
  - name: intercom-api
    description: Endpoints related to intercom APIs
  - name: jobs-v3
  - name: llm-gateway-v3
  - name: auth-login
  - name: auth-logout
  - name: metrics-v3
    description: Metrics endpoints
  - name: model-v3
  - name: dashboard-v3
  - name: model-deployment-v3
  - name: monitoring-summary-v3
  - name: histograms-v3
  - name: organization-roles-v3
    description: Update user org role
  - name: organization-settings-v3
    description: Update organization settings such as timezone, email configuration, etc.
  - name: pagerduty-api
    description: CRUD for Pagerduty services.
  - name: project-v3
  - name: project-roles-v3
    description: Project role assignment management
  - name: searchable-text-key-v3
    description: >-
      Manage the global searchable text keys table that controls which OTel
      attribute keys are routed to the full-text-searchable `ValueContent`
      column in the unified attributes table. Changes propagate to the backing
      ClickHouse dictionary within 1-2 minutes and affect all tenants.
  - name: segments-v3
  - name: semantic-mapping-v3
    description: >-
      Manage the global semantic name mappings table that maps raw OTel
      attribute keys to canonical semantic concepts. Changes propagate to the
      backing ClickHouse dictionary within 1-2 minutes and affect all tenants.
  - name: server-info-v3
    description: Endpoints related to retrieving server information
  - name: sessions-v3
    description: v3 session APIs
  - name: team-roles-v3
  - name: team-v3
  - name: traces-v3
    description: v3 trace api for monitoring
  - name: fetch-sessions-v3
    description: v3 fetch sessions api for monitoring
  - name: user-access-key
    description: >
      CRUD operations for user API keys. All endpoints are user-scoped — each
      user can only operate on their own API keys. No one including Org admins
      have access to other users' API keys.
  - name: users-v3
  - name: version-compatibility-v3
  - name: webhooks
externalDocs:
  url: https://docs.fiddler.ai
  description: Find out more about Fiddler
paths:
  /v3/evals/datasets/{dataset_id}/schema:
    parameters:
      - name: dataset_id
        in: path
        description: Dataset UUID
        required: true
        schema:
          type: string
          format: uuid
    get:
      tags:
        - evals
        - datasets
      summary: Get dataset schema
      description: >-
        Discover what field keys exist in each JSON bucket (inputs,
        expected_outputs, metadata, extras) across this dataset's items, along
        with a coverage count and inferred data type for each key. Useful for
        pre-populating a field mapper UI or for an MCP agent to understand what
        data is available before constructing a mapping. Returns empty objects
        for all buckets if the dataset has no items.
      operationId: getEvalsDatasetSchemaV3
      responses:
        '200':
          description: Dataset schema per bucket
          content:
            application/json:
              schema:
                allOf:
                  - $ref: '#/components/schemas/ApiResponse'
                  - type: object
                    properties:
                      data:
                        $ref: '#/components/schemas/DatasetSchema'
              example:
                data:
                  total_items: 500
                  sampled: false
                  inputs:
                    question:
                      count: 500
                      data_type: STRING
                    context:
                      count: 423
                      data_type: STRING
                  expected_outputs:
                    answer:
                      count: 500
                      data_type: STRING
                  metadata:
                    trace_id:
                      count: 500
                      data_type: STRING
                    model:
                      count: 500
                      data_type: STRING
                  extras:
                    cost_usd:
                      count: 120
                      data_type: FLOAT
                api_version: '3.0'
                kind: NORMAL
        '401':
          $ref: '#/components/responses/401'
        '403':
          $ref: '#/components/responses/403'
        '404':
          $ref: '#/components/responses/404'
        '500':
          $ref: '#/components/responses/500'
components:
  schemas:
    ApiResponse:
      type: object
      description: |
        Response object for standard API responses.
      properties:
        api_version:
          type: string
          default: '3.0'
          enum:
            - '2.0'
            - '3.0'
          description: |
            API version.
        kind:
          type: string
          default: NORMAL
          enum:
            - NORMAL
          description: |
            Type of response, indicating a normal response.
    DatasetSchema:
      type: object
      description: >-
        Schema of existing dataset items. Each bucket maps field keys to their
        coverage count and inferred type. Empty objects indicate no items exist
        for that bucket or no keys were found within it.
      required:
        - total_items
        - sampled
        - inputs
        - expected_outputs
        - metadata
        - extras
      properties:
        total_items:
          type: integer
          description: >-
            Number of items used to compute the schema. When sampled is true
            this is capped and counts are approximate; when sampled is false
            this is the exact item count for the dataset.
        sampled:
          type: boolean
          description: >-
            True when the result is based on a sample of a larger item set.
            Counts are approximate in this case.
        inputs:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/DatasetFieldCoverage'
          description: Keys found in the inputs bucket across sampled items.
          example:
            question:
              count: 500
              data_type: STRING
            context:
              count: 423
              data_type: STRING
        expected_outputs:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/DatasetFieldCoverage'
          description: Keys found in the expected_outputs bucket across sampled items.
          example:
            answer:
              count: 500
              data_type: STRING
        metadata:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/DatasetFieldCoverage'
          description: Keys found in the metadata bucket across sampled items.
          example:
            trace_id:
              count: 500
              data_type: STRING
            model:
              count: 500
              data_type: STRING
        extras:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/DatasetFieldCoverage'
          description: Keys found in the extras bucket across sampled items.
          example:
            cost_usd:
              count: 120
              data_type: FLOAT
    DatasetFieldCoverage:
      type: object
      description: Coverage and inferred type for a single field key within a bucket.
      required:
        - count
        - data_type
      properties:
        count:
          type: integer
          description: >-
            Number of items (within the sample) that have this key set. Divide
            by total_items to get the coverage ratio.
        data_type:
          type: string
          enum:
            - STRING
            - FLOAT
          description: >-
            Inferred data type of the field value across the sampled items.
            FLOAT when all observed values are numeric; STRING otherwise.
            Conflicts default to STRING.
    ErrorResponse:
      type: object
      description: |
        Response object for errors returned by the API.
      properties:
        api_version:
          type: string
          default: '3.0'
          enum:
            - '2.0'
            - '3.0'
          description: |
            API version of the response.
        kind:
          type: string
          default: ERROR
          enum:
            - ERROR
          description: |
            Type of response, usually indicating an error.
        error:
          type: object
          properties:
            code:
              type: integer
              format: int32
              description: >
                Represents the code for this error, typically an HTTP response
                code.
              default: 400
              enum:
                - 400
                - 403
                - 404
                - 500
            message:
              type: string
              description: >
                A human-readable message providing more details about the error.
                If there are multiple errors, it will be the message for the
                first error.
              example: Resource Not Found
            errors:
              type: array
              description: >
                Container for additional information regarding the error,
                especially for multiple errors.
              items:
                type: object
                properties:
                  reason:
                    type: string
                    description: >
                      Unique identifier for this error, different from the error
                      code.
                    example: ResourceNotFoundException
                  message:
                    type: string
                    description: >
                      A human-readable message providing more details about the
                      error. If there is only one error, this field will match
                      error.message.
                    example: Resource Not Found
                  help:
                    type: string
                    description: >
                      Link to support or documentation providing more
                      information on the error.
  responses:
    '401':
      description: Unauthorized
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
    '403':
      description: Forbidden
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
    '404':
      description: Resource not found
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
    '500':
      description: Internal Server Error
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
  securitySchemes:
    BearerAuth:
      type: http
      scheme: bearer

````