diff --git a/annif/openapi/annif.yaml b/annif/openapi/annif.yaml
index 6412280d..7f86f65f 100644
--- a/annif/openapi/annif.yaml
+++ b/annif/openapi/annif.yaml
@@ -195,13 +195,13 @@ paths:
               type: object
               required:
               - text
-              - candidates
+              - languages
               properties:
                 text:
                   type: string
                   description: input text
                   example: A quick brown fox jumped over the lazy dog.
-                candidates:
+                languages:
                   type: array
                   description: candidate languages as IETF BCP 47 codes
                   items:
@@ -209,6 +209,8 @@ paths:
                     maxLength: 3
                     minLength: 2
                     example: en
+                  minItems: 1
+                  maxItems: 5
         required: true
       responses:
         200:
diff --git a/annif/rest.py b/annif/rest.py
index c283a60b..18d5ecfe 100644
--- a/annif/rest.py
+++ b/annif/rest.py
@@ -87,16 +87,9 @@ def detect_language(body: dict[str, Any]):
     """return scores for detected languages formatted according to Swagger spec"""
 
     text = body.get("text")
-    candidates = body.get("candidates")
+    languages = body.get("languages")
 
-    if not candidates:
-        return connexion.problem(
-            status=400,
-            title="Bad Request",
-            detail="no candidate languages given",
-        )
-
-    detector = get_language_detector(tuple(candidates))
+    detector = get_language_detector(tuple(languages))
     try:
         proportions = detector.proportion_in_each_language(text)
     except ValueError:
diff --git a/tests/test_openapi.py b/tests/test_openapi.py
index 76f33695..4b409c5d 100644
--- a/tests/test_openapi.py
+++ b/tests/test_openapi.py
@@ -126,3 +126,15 @@ def test_openapi_learn_novocab(app_client):
     data = []
     req = app_client.post("http://localhost:8000/v1/projects/novocab/learn", json=data)
     assert req.status_code == 503
+
+
+def test_rest_detect_language_no_candidates(app_client):
+    data = {"text": "example text", "languages": []}
+    req = app_client.post("http://localhost:8000/v1/detect-language", json=data)
+    assert req.status_code == 400
+
+
+def test_rest_detect_language_too_many_candidates(app_client):
+    data = {"text": "example text", "languages": ["en", "fr", "de", "it", "es", "nl"]}
+    req = app_client.post("http://localhost:8000/v1/detect-language", json=data)
+    assert req.status_code == 400
diff --git a/tests/test_rest.py b/tests/test_rest.py
index ef32a9cc..43d42d78 100644
--- a/tests/test_rest.py
+++ b/tests/test_rest.py
@@ -57,7 +57,7 @@ def test_rest_detect_language_english(app):
     # english text should be detected
     with app.app_context():
         result = annif.rest.detect_language(
-            {"text": "example text", "candidates": ["en", "fi", "sv"]}
+            {"text": "example text", "languages": ["en", "fi", "sv"]}
         )[0]
         assert {"language": "en", "score": 1} in result["results"]
 
@@ -66,27 +66,21 @@ def test_rest_detect_language_unknown(app):
     # an unknown language should return None
     with app.app_context():
         result = annif.rest.detect_language(
-            {"text": "exampley texty", "candidates": ["fi", "sv"]}
+            {"text": "exampley texty", "languages": ["fi", "sv"]}
         )[0]
         assert {"language": None, "score": 1} in result["results"]
 
 
 def test_rest_detect_language_no_text(app):
     with app.app_context():
-        result = annif.rest.detect_language({"text": "", "candidates": ["en"]})[0]
+        result = annif.rest.detect_language({"text": "", "languages": ["en"]})[0]
         assert {"language": None, "score": 1} in result["results"]
 
 
-def test_rest_detect_language_no_candidates(app):
-    with app.app_context():
-        result = annif.rest.detect_language({"text": "example text", "candidates": []})
-        assert result.status_code == 400
-
-
 def test_rest_detect_language_unsupported_candidates(app):
     with app.app_context():
         result = annif.rest.detect_language(
-            {"text": "example text", "candidates": ["unk"]}
+            {"text": "example text", "languages": ["unk"]}
         )
         assert result.status_code == 400