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

# Domain

> Retrieve detailed metadata for a single top-level research domain by its numeric ID.

Retrieves a top-level research domain (Level 0 taxonomy node) by its numeric identifier (e.g. `3` for Physical Sciences).

### Path Parameters

<ParamField path="id" type="string" required>
  Unique numeric domain identifier (e.g. `3`).
</ParamField>

### Response Fields

<ResponseField name="id" type="string" required>
  Numeric domain identifier (e.g. `"3"`).
</ResponseField>

<ResponseField name="name" type="string" required>
  Domain display name (e.g. `"Physical Sciences"`).
</ResponseField>

<ResponseField name="description" type="string">
  Scope description.
</ResponseField>

<ResponseField name="display_name_alternatives" type="array">
  Alternative display names or abbreviations.
</ResponseField>

<ResponseField name="fields" type="array">
  Child research fields.

  <Expandable title="fields attributes">
    <ResponseField name="id" type="integer">Field numeric ID.</ResponseField>
    <ResponseField name="name" type="string">Field display name.</ResponseField>
  </Expandable>
</ResponseField>

<ResponseField name="siblings" type="array">
  Sibling domains.

  <Expandable title="siblings attributes">
    <ResponseField name="id" type="integer">Sibling domain numeric ID.</ResponseField>
    <ResponseField name="name" type="string">Sibling domain display name.</ResponseField>
  </Expandable>
</ResponseField>

<ResponseField name="outputs_count" type="integer">
  Total number of indexed outputs in this domain.
</ResponseField>

<ResponseField name="cited_by_count" type="integer">
  Total citation count received.
</ResponseField>

<ResponseField name="ids" type="object">
  External identifiers.

  <Expandable title="ids attributes">
    <ResponseField name="wikidata" type="string">Wikidata URL.</ResponseField>
    <ResponseField name="wikipedia" type="string">Wikipedia URL.</ResponseField>
  </Expandable>
</ResponseField>

<ResponseField name="updated_date" type="string">
  Last updated timestamp.
</ResponseField>

<ResponseField name="created_date" type="string">
  Creation timestamp.
</ResponseField>

<RequestExample>
  ```bash cURL theme={null}
  curl -X GET "https://api.hexagraph.in/domains/3"
  ```

  ```javascript JavaScript theme={null}
  fetch("https://api.hexagraph.in/domains/3")
    .then(response => response.json())
    .then(data => console.log(data));
  ```

  ```python Python theme={null}
  import requests

  response = requests.get("https://api.hexagraph.in/domains/3")
  print(response.json())
  ```

  ```go Go theme={null}
  package main

  import (
  	"fmt"
  	"io"
  	"net/http"
  )

  func main() {
  	resp, err := http.Get("https://api.hexagraph.in/domains/3")
  	if err != nil {
  		fmt.Println("Error:", err)
  		return
  	}
  	defer resp.Body.Close()
  	body, _ := io.ReadAll(resp.Body)
  	fmt.Println(string(body))
  }
  ```
</RequestExample>

<ResponseExample>
  ```json 200 OK theme={null}
  {
    "id": 3,
    "name": "Physical Sciences",
    "description": "branch of natural science that studies non-living systems",
    "ids": {
      "wikidata": "https://www.wikidata.org/wiki/Q14632398",
      "wikipedia": "https://en.wikipedia.org/wiki/Outline_of_physical_science"
    },
    "display_name_alternatives": ["Natural Sciences"],
    "fields": [
      {
        "id": 15,
        "name": "Chemical Engineering"
      }
    ],
    "siblings": [
      {
        "id": 1,
        "name": "Life Sciences"
      }
    ],
    "outputs_count": 163713213,
    "cited_by_count": 1132994559,
    "updated_date": "2026-08-05T03:01:47",
    "created_date": "2024-01-23T15:21:58"
  }
  ```

  ```json 404 Not Found theme={null}
  {
    "statusCode": 404,
    "message": "Domain with ID 999 not found",
    "error": "Not Found"
  }
  ```

  ```json 429 Too Many Requests theme={null}
  {
    "statusCode": 429,
    "error": "Too Many Requests",
    "message": "IP rate limit exceeded (max 30 requests per minute). Please try again in 42 seconds (at 11:40:32 UTC).",
    "reset_in_seconds": 42,
    "reset_at_utc": "2026-08-05T11:40:32.000Z"
  }
  ```
</ResponseExample>