# 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.