> For the complete documentation index, see [llms.txt](https://docs.b2ihealthcare.com/snow-owl/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.b2ihealthcare.com/snow-owl/quick-start/find-concepts-using-ecl.md).

# Find concepts using ECL

One of Snow Owl's powerful features is the ability to list concepts matching a user-specified query expression using SNOMED International's Expression Constraint Language (ECL) syntax. If you would like to know more about the language itself, visit [the documentation](https://confluence.ihtsdotools.org/display/DOCECL/Expression+Constraint+Language+-+Specification+and+Guide) on the official site.

In this example, we list the direct descendants of the root concept using the ECL expression `<!138875005` (via the `ecl` query parameter), and also limit the result set to a single item using the `limit` query parameter:

```bash
curl -u "test:test" 'http://localhost:8080/snowowl/snomedct/SNOMEDCT/concepts?ecl=%3C!138875005&limit=1&pretty'
```

As no query parameter in this request would make Snow Owl differentiate between "better" and "worse" results (eg. a search term to match), concepts in the response will be sorted by identifier.

The item returned is, indeed, one of the top-level concepts in SNOMED CT: \
`105590001 |Substance|`

```json
{
  "items": [ {
    "id": "105590001",
    "released": true,
    "active": true,
    "effectiveTime": "20020131",
    "moduleId": "900000000000207008",
    "iconId": "substance",
    "score": 0.0,
    "memberOf": [ "723560006", "733073007", "900000000000497000" ],
    "activeMemberOf": [ "723560006", "733073007", "900000000000497000" ],
    "definitionStatus": {
      "id": "900000000000074008"
    },
    "subclassDefinitionStatus": "NON_DISJOINT_SUBCLASSES",
    "ancestorIds": [ "-1" ],
    "parentIds": [ "138875005" ],
    "statedAncestorIds": [ "-1" ],
    "statedParentIds": [ "138875005" ],
    "definitionStatusId": "900000000000074008"
  } ],
  "searchAfter": "AoEpMTA1NTkwMDAx",
  "limit": 1,
  "total": 19
}
```

The number `19` in property `total` suggests that additional matches exist that were not included in the response this time.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.b2ihealthcare.com/snow-owl/quick-start/find-concepts-using-ecl.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.