Single Catalog Category

Status: stable Category: catalog Added: 2026-04-20 Last reviewed: 2026-04-21

Summary

Returns one category — identified by ?name= — with its nested resources and operations. Use this when you already know which category you want; it returns less data than /api/catalog/categories and no more work than /api/catalog/get.

Endpoint

Field	Value
Method	`GET`
Path	`/api/catalog/category`
Full URL	`https://engine.tripod-health.com/api/catalog/category`
Authentication	API key (required)
Request body	none
Response body	`application/json`
Idempotent	Yes
Rate-limited	Yes

Purpose

Direct lookup when you know the category name. Cheaper and easier to consume than slicing it out of the full catalog.
Verifying a category exists before constructing URLs that depend on it.
Fetching audience-specific labels for just one category. Pair with ?audience= and you get the labels you need without paying for the whole catalog.

Authentication

Send a valid API key in the apikey header. See authentication.md.

Request

Headers

Header	Required	Description
`apikey`	Yes	Consumer API key.
`X-Request-ID`	No	Optional correlation ID. Echoed in the `X-Request-ID` response header.

Path parameters

None.

Query parameters

Parameter	Type	Required	Default	Description
`name`	`string`	Yes	—	Category name (for example `"pain"`, `"function"`). Must match a registered category exactly — lookup is case-sensitive.
`audience`	`string`	No	none	One of `employee`, `employer`, `provider`. Replaces the category's (and nested resources' and operations') `display_name` with that audience's alias, falling back to canonical labels when no alias is registered.

Body

None.

Response

Success — `200 OK`

The response is a single category object, identical in shape to one element of the categories[] array from /api/catalog/categories:

{
  "name": "pain",
  "display_name": "Pain",
  "aliases": {
    "employee": "Pain Level",
    "employer": "Pain",
    "provider": "Pain"
  },
  "description": "Subjective pain intensity and pain-oriented screening tools.",
  "version": "0.1.0",
  "last_updated": "2026-04-17",
  "resources": [
    {
      "name": "orebro",
      "display_name": "Orebro Musculoskeletal Pain Screening",
      "aliases": {
        "employee": "Pain Screening Questionnaire",
        "employer": "Musculoskeletal Pain Screening",
        "provider": "Orebro"
      },
      "description": "Orebro Musculoskeletal Pain Screening Questionnaire (OMPSQ): multi-item screening that returns a total score and a risk profile.",
      "version": "0.1.0",
      "last_updated": "2026-04-17",
      "operations": [
        { "name": "questions", "display_name": "Questions", "aliases": {}, "description": "Return the instrument's items, ordering, and answer choices so the caller can render or present them.", "version": "0.1.0", "last_updated": "2026-04-17", "http_method": "GET" },
        { "name": "score", "display_name": "Score", "aliases": {}, "description": "Submit responses to the instrument and receive its score (and profile, where the instrument supports classification).", "version": "0.1.0", "last_updated": "2026-04-17", "http_method": "POST" }
      ]
    }
  ]
}

Response fields

Same as one element of the categories[] array from /api/catalog/categories. Key fields:

Field	Type	Always present	Description
`name`	`string`	Yes	Category identifier used in paths.
`display_name`	`string`	Yes	Canonical label, or the audience alias when `?audience=` was set.
`aliases`	`object`	Yes	Audience-to-label map. May be `{}`.
`description`	`string`	Yes	One-sentence description of the category.
`version`	`string` (SemVer)	Yes	Category-level version.
`last_updated`	`string` (ISO date)	Yes	Last structural change.
`resources`	`array`	Yes	Resources in this category. Each follows the resource shape documented in `/api/catalog/resources` (except without `category` / `path_prefix` — see below).

Status codes

Code	Meaning	When
`200`	OK	Category returned.
`400`	`ValidationError`	`name` was not provided. Also emitted when `audience` is not one of the allowed values. `field` names the offending parameter.
`401`	`Unauthenticated`	Missing or invalid API key.
`404`	`NotFound`	No category with that `name` is registered.
`429`	`RateLimited`	Per-consumer rate limit exceeded.

Examples

The language-specific invocations below assume the call() helper (or its equivalent) from quickstart.md.

1. Canonical request and response

Send:

GET /api/catalog/category?name=pain HTTP/1.1
Host: engine.tripod-health.com
apikey: $ENGINE_API_KEY
X-Request-ID: docs-catalog-category-canonical

Receive (200 OK):

{
  "name": "pain",
  "display_name": "Pain",
  "aliases": {
    "employee": "Pain Level",
    "employer": "Pain",
    "provider": "Pain"
  },
  "description": "Subjective pain intensity and pain-oriented screening tools.",
  "version": "0.1.0",
  "last_updated": "2026-04-17",
  "resources": [
    {
      "name": "orebro",
      "display_name": "Orebro Musculoskeletal Pain Screening",
      "aliases": {
        "employee": "Pain Screening Questionnaire",
        "employer": "Musculoskeletal Pain Screening",
        "provider": "Orebro"
      },
      "description": "Orebro Musculoskeletal Pain Screening Questionnaire (OMPSQ): multi-item screening that returns a total score and a risk profile.",
      "version": "0.1.0",
      "last_updated": "2026-04-17",
      "operations": [
        {
          "name": "questions",
          "display_name": "Questions",
          "aliases": {},
          "description": "Return the instrument's items, ordering, and answer choices so the caller can render or present them.",
          "version": "0.1.0",
          "last_updated": "2026-04-17",
          "http_method": "GET"
        },
        {
          "name": "score",
          "display_name": "Score",
          "aliases": {},
          "description": "Submit responses to the instrument and receive its score (and profile, where the instrument supports classification).",
          "version": "0.1.0",
          "last_updated": "2026-04-17",
          "http_method": "POST"
        }
      ]
    }
  ]
}

The live pain category today carries two resources (orebro, pain_scale); only the first is shown above.

2. Calling the endpoint in your language

curl

# Canonical labels
curl -sS "https://engine.tripod-health.com/api/catalog/category?name=pain" \
  -H "apikey: $ENGINE_API_KEY"

# Employee-facing labels. display_name on the category becomes "Pain Level";
# every nested resource's display_name uses its employee alias. Canonical
# labels remain in the aliases map.
curl -sS "https://engine.tripod-health.com/api/catalog/category?name=function&audience=employee" \
  -H "apikey: $ENGINE_API_KEY"

Python (`requests`)

# Uses the call() + EngineError from quickstart.md.
try:
    cat = call("GET", "/api/catalog/category?name=function&audience=provider")
except EngineError as e:
    if e.status == 404:
        raise RuntimeError("function category is not registered in this deploy")
    raise

for res in cat["resources"]:
    print(f"  {res['display_name']}  (/api/{cat['name']}/{res['name']})")

Node.js (native `fetch`)

// Uses the call() + EngineError from quickstart.md.
try {
  const cat = await call("GET", "/api/catalog/category?name=pain");
  for (const res of cat.resources) {
    console.log(`  ${res.display_name}  (/api/${cat.name}/${res.name})`);
  }
} catch (e) {
  if (e.status === 404) console.warn("pain category not registered");
  else throw e;
}

TypeScript

// Uses the typed call<T>() helper from quickstart.md.
// The CatalogCategory type is the same one shown in catalog-categories.md.
const category = await call<CatalogCategory>(
  "GET",
  "/api/catalog/category?name=pain&audience=provider",
);

Go

// Uses the call() helper from quickstart.md.
cat, err := call("GET", "/api/catalog/category?name=pain", nil, 3)
if err != nil {
    if ee, ok := err.(*EngineError); ok && ee.Status == 404 {
        log.Println("pain category not registered")
        return
    }
    panic(err)
}
fmt.Println(cat["display_name"])

Java

// Uses the call() helper from quickstart.md.
try {
    String cat = call("GET", "/api/catalog/category?name=pain", null, 3);
    System.out.println(extract(cat, "display_name"));
} catch (EngineException e) {
    if (e.status == 404) System.err.println("pain category not registered");
    else throw e;
}

C# (.NET `HttpClient`)

// Uses the Call() helper from quickstart.md.
try
{
    var cat = await Call(HttpMethod.Get, "/api/catalog/category?name=pain");
    Console.WriteLine(cat.GetProperty("display_name").GetString());
}
catch (HttpRequestException ex) when (ex.Message.Contains("404"))
{
    Console.Error.WriteLine("pain category not registered");
}

PowerShell

# Uses the Invoke-Engine helper from quickstart.md.
try {
    $cat = Invoke-Engine -Method Get -Path "/api/catalog/category?name=pain"
    $cat.display_name
} catch {
    if ($_.Exception.Message -match "404") {
        Write-Warning "pain category not registered"
    } else { throw }
}

3. Error scenarios

Missing `name`

Send:

curl -sS "https://engine.tripod-health.com/api/catalog/category" \
  -H "apikey: $ENGINE_API_KEY" \
  -H "X-Request-ID: docs-catalog-category-missing-name" \
  -w "\nHTTP %{http_code}\n"

Receive (400):

{
  "timestamp": "2026-04-21T23:05:31.464Z",
  "error": "ValidationError",
  "message": "Query parameter 'name' is required",
  "field": "name",
  "request_id": "docs-catalog-category-missing-name"
}

Unknown category

Send:

curl -sS "https://engine.tripod-health.com/api/catalog/category?name=frobnitz" \
  -H "apikey: $ENGINE_API_KEY" \
  -H "X-Request-ID: docs-catalog-category-unknown" \
  -w "\nHTTP %{http_code}\n"

Receive (404):

{
  "timestamp": "2026-04-21T23:05:31.850Z",
  "error": "NotFound",
  "message": "Category 'frobnitz' is not registered",
  "request_id": "docs-catalog-category-unknown"
}

Invalid audience

Send:

curl -sS "https://engine.tripod-health.com/api/catalog/category?name=pain&audience=bogus" \
  -H "apikey: $ENGINE_API_KEY" \
  -H "X-Request-ID: docs-catalog-category-bad-audience" \
  -w "\nHTTP %{http_code}\n"

Receive (400):

{
  "timestamp": "2026-04-21T23:05:32.240Z",
  "error": "ValidationError",
  "message": "Unknown audience 'bogus'. Valid values: employee, employer, provider.",
  "field": "audience",
  "request_id": "docs-catalog-category-bad-audience"
}

Intended use

Validating a category name before constructing URLs. A 200 confirms the category exists and gives you the resources inside it.
Rendering a single category's details. A UI drilling into a category can fetch just that category instead of the full catalog.
Checking whether a category's version or last_updated has moved without pulling the full tree.

Mistaken use

Do not pass ?name= with the category's display_name value. The lookup is on the canonical name field (URL-safe identifier like "pain", "rtw_belief"), not on the human-readable label. Passing "Pain Severity" returns 404.
Do not use this to discover which categories exist. Use /api/catalog/categories. A negative result from /category?name=X cannot distinguish "X was removed" from "X never existed."
Do not URL-decode name expecting Trinity to tolerate synonyms. The match is exact, byte-for-byte.
Do not assume resources[] is sorted alphabetically. Resources appear in catalog declaration order within the category. Sort client-side if you need a specific order.

Debugging

Capture the X-Request-ID response header.
400 ValidationError with field: "name" — you did not include ?name= in the query string, or it was empty.
400 ValidationError with field: "audience" — audience was set to something other than employee, employer, provider.
404 NotFound — the category does not exist in the current deploy. Cross-reference with /api/catalog/categories to see which categories are live; check /api/version/get to see which deploy you are hitting.
Category exists but nested resources look wrong. Check the version and last_updated fields on the category and its resources — something may have moved between your cache and the current deploy.

Rate limits

See rate-limits.md.

GET /api/catalog/get — full catalog tree.
GET /api/catalog/categories — all categories at once.
GET /api/catalog/resource — single resource by ?name=, optionally scoped by ?category=.

Change history

Date	Change
2026-04-20	Initial publication.

Summary​

Endpoint​

Purpose​

Authentication​

Request​

Headers​

Path parameters​

Query parameters​

Body​

Response​

Success — 200 OK​

Response fields​

Status codes​

Examples​

1. Canonical request and response​

2. Calling the endpoint in your language​

curl​

Python (requests)​

Node.js (native fetch)​

TypeScript​

Go​

Java​

C# (.NET HttpClient)​

PowerShell​

3. Error scenarios​

Missing name​

Unknown category​

Invalid audience​

Intended use​

Mistaken use​

Debugging​

Rate limits​

Related endpoints​

Change history​

Summary

Endpoint

Purpose

Authentication

Request

Headers

Path parameters

Query parameters

Body

Response

Success — `200 OK`

Response fields

Status codes

Examples

1. Canonical request and response

2. Calling the endpoint in your language

curl

Python (`requests`)

Node.js (native `fetch`)

TypeScript

Go

Java

C# (.NET `HttpClient`)

PowerShell

3. Error scenarios

Missing `name`

Unknown category

Invalid audience

Intended use

Mistaken use

Debugging

Rate limits

Related endpoints

Change history