> ## Documentation Index > Fetch the complete documentation index at: https://developers.openalex.org/llms.txt > Use this file to discover all available pages before exploring further. # Get a single domain > Retrieve a single domain by its ID (1-4). ## OpenAPI ````yaml /api-reference/openapi.json get /domains/{id} openapi: 3.1.0 info: title: OpenAlex API description: >- The OpenAlex API provides access to a comprehensive catalog of scholarly works, authors, sources, institutions, topics, keywords, publishers, and funders. OpenAlex indexes over 250 million scholarly works. version: 1.0.0 contact: name: OpenAlex Support email: support@openalex.org url: https://openalex.org license: name: CC0 url: https://creativecommons.org/publicdomain/zero/1.0/ servers: - url: https://api.openalex.org description: OpenAlex Production API security: - apiKey: [] tags: - name: Works description: Scholarly documents like journal articles, books, datasets, and theses - name: Authors description: People who create scholarly works - name: Sources description: Journals, repositories, and other venues where works are hosted - name: Institutions description: Universities, research organizations, and other affiliations - name: Topics description: Research topics automatically assigned to works - name: Keywords description: Short phrases identified from works' topics - name: Publishers description: Companies and organizations that publish scholarly works - name: Funders description: Organizations that fund research - name: Autocomplete description: Fast typeahead search for any entity type - name: Domains description: Top-level categories in the topic hierarchy (4 total) - name: Fields description: Second-level categories in the topic hierarchy (26 total) - name: Subfields description: Third-level categories in the topic hierarchy (254 total) - name: SDGs description: UN Sustainable Development Goals (17 total) - name: Countries description: Geographic countries for filtering research by location - name: Continents description: Geographic continents (7 total) - name: Languages description: Languages of scholarly works - name: Awards description: Research grants and funding awards - name: Concepts description: Legacy taxonomy of research areas (deprecated - use Topics instead) - name: Work Types description: Types of scholarly works (article, book, dataset, etc.) - name: Source Types description: Types of sources (journal, repository, conference, etc.) - name: Institution Types description: Types of institutions (education, healthcare, company, etc.) - name: Licenses description: Open access licenses (CC BY, CC BY-SA, etc.) paths: /domains/{id}: get: tags: - Domains summary: Get a single domain description: Retrieve a single domain by its ID (1-4). operationId: getDomain parameters: - name: id in: path required: true description: Domain ID (1-4) schema: type: string examples: lifesciences: value: '1' summary: Life Sciences socialsciences: value: '2' summary: Social Sciences - $ref: '#/components/parameters/select' - $ref: '#/components/parameters/api_key' responses: '200': description: Successful response content: application/json: schema: $ref: '#/components/schemas/Domain' '404': $ref: '#/components/responses/NotFound' '429': $ref: '#/components/responses/RateLimited' components: parameters: select: name: select in: query description: >- Comma-separated list of fields to return. Reduces response size. Example: `select=id,display_name,cited_by_count` schema: type: string api_key: name: api_key in: query description: >- Your OpenAlex API key (required). Get a free key at https://openalex.org/settings/api required: true schema: type: string schemas: Domain: type: object description: Top-level category in the topic hierarchy (4 total) properties: id: type: string example: https://openalex.org/domains/1 description: The OpenAlex ID for this domain. display_name: type: string description: The English-language label of the domain. description: type: string description: A description of this domain. display_name_alternatives: type: array items: type: string description: Alternate names for this domain. fields: type: array items: type: object properties: id: type: string display_name: type: string description: >- The fields within this domain. Each object has `id` and `display_name`. siblings: type: array items: type: object properties: id: type: string display_name: type: string description: >- Other domains at the same level. Each object has `id` and `display_name`. ids: type: object properties: openalex: type: string wikidata: type: string wikipedia: type: string description: 'External identifiers:' works_count: type: integer description: The number of works tagged with topics in this domain. cited_by_count: type: integer description: Total citations to works in this domain. works_api_url: type: string description: A URL that returns all works tagged with this domain. created_date: type: string format: date description: When this domain was added to OpenAlex (ISO 8601 date). updated_date: type: string format: date-time description: When this domain was last updated (ISO 8601 datetime). Error: type: object properties: error: type: string description: Error type message: type: string description: Human-readable error message responses: NotFound: description: Entity not found content: application/json: schema: $ref: '#/components/schemas/Error' RateLimited: description: Rate limit exceeded content: application/json: schema: $ref: '#/components/schemas/Error' securitySchemes: apiKey: type: apiKey in: query name: api_key description: >- Your OpenAlex API key. Get a free key at https://openalex.org/settings/api ````