diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/query/api/StructuredQuery.java b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/StructuredQuery.java
index b5b380af..bb540911 100644
--- a/src/main/java/de/numcodex/feasibility_gui_backend/query/api/StructuredQuery.java
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/StructuredQuery.java
@@ -4,6 +4,7 @@
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import de.numcodex.feasibility_gui_backend.common.api.Criterion;
+import de.numcodex.feasibility_gui_backend.common.api.TermCode;
 import de.numcodex.feasibility_gui_backend.query.api.validation.StructuredQueryValidation;
 import lombok.Builder;
 
diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/query/api/ValidatedStructuredQuery.java b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/ValidatedStructuredQuery.java
new file mode 100644
index 00000000..799185e7
--- /dev/null
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/ValidatedStructuredQuery.java
@@ -0,0 +1,15 @@
+package de.numcodex.feasibility_gui_backend.query.api;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import de.numcodex.feasibility_gui_backend.common.api.Criterion;
+import lombok.Builder;
+
+import java.util.List;
+
+@Builder
+public record ValidatedStructuredQuery(
+    @JsonProperty StructuredQuery query,
+    @JsonProperty List<Criterion> invalidCriteria
+) {
+
+}
diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/query/api/validation/StructuredQueryValidator.java b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/validation/StructuredQueryValidator.java
index 986514c3..116fd67b 100644
--- a/src/main/java/de/numcodex/feasibility_gui_backend/query/api/validation/StructuredQueryValidator.java
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/query/api/validation/StructuredQueryValidator.java
@@ -13,6 +13,8 @@
 import jakarta.validation.ConstraintValidatorContext;
 import org.springframework.beans.factory.annotation.Qualifier;
 
+import java.util.stream.Collectors;
+
 /**
  * Validator for {@link StructuredQuery} that does an actual check based on a JSON schema.
  */
@@ -47,8 +49,11 @@ public boolean isValid(StructuredQuery structuredQuery,
       var jsonSubject = new JSONObject(jsonUtil.writeValueAsString(structuredQuery));
       jsonSchema.validate(jsonSubject);
       return true;
-    } catch (ValidationException | JsonProcessingException e) {
-      log.debug("Structured query is invalid", e);
+    } catch (ValidationException e) {
+      log.error("Structured query is invalid: {}", e.getCausingExceptions().stream().map(Throwable::getMessage).collect(Collectors.joining(" ## ")));
+      return false;
+    } catch (JsonProcessingException jpe) {
+      log.debug("Could not process JSON", jpe);
       return false;
     }
   }
diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestController.java b/src/main/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestController.java
index cfa6dfaa..a84f9a6a 100644
--- a/src/main/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestController.java
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestController.java
@@ -6,12 +6,7 @@
 import de.numcodex.feasibility_gui_backend.query.QueryHandlerService;
 import de.numcodex.feasibility_gui_backend.query.QueryHandlerService.ResultDetail;
 import de.numcodex.feasibility_gui_backend.query.QueryNotFoundException;
-import de.numcodex.feasibility_gui_backend.query.api.Query;
-import de.numcodex.feasibility_gui_backend.query.api.QueryListEntry;
-import de.numcodex.feasibility_gui_backend.query.api.QueryResult;
-import de.numcodex.feasibility_gui_backend.query.api.QueryResultRateLimit;
-import de.numcodex.feasibility_gui_backend.query.api.SavedQuery;
-import de.numcodex.feasibility_gui_backend.query.api.StructuredQuery;
+import de.numcodex.feasibility_gui_backend.query.api.*;
 import de.numcodex.feasibility_gui_backend.query.api.status.FeasibilityIssue;
 import de.numcodex.feasibility_gui_backend.query.api.status.FeasibilityIssues;
 import de.numcodex.feasibility_gui_backend.query.api.status.SavedQuerySlots;
@@ -404,9 +399,14 @@ public ResponseEntity<Object> getQueryContent(
   }
 
   @PostMapping("/validate")
-  public ResponseEntity<Object> validateStructuredQuery(
+  public ResponseEntity<ValidatedStructuredQuery> validateStructuredQuery(
       @Valid @RequestBody StructuredQuery query) {
-    return new ResponseEntity<>(HttpStatus.NO_CONTENT);
+    var invalidCriteria = termCodeValidation.getInvalidCriteria(query);
+    var validatedQuery = ValidatedStructuredQuery.builder()
+        .query(query)
+        .invalidCriteria(invalidCriteria)
+        .build();
+    return new ResponseEntity<>(validatedQuery, HttpStatus.OK);
   }
 
   private boolean hasAccess(Long queryId, Authentication authentication) {
diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/terminology/validation/TermCodeValidation.java b/src/main/java/de/numcodex/feasibility_gui_backend/terminology/validation/TermCodeValidation.java
index 245c2e27..48e21858 100644
--- a/src/main/java/de/numcodex/feasibility_gui_backend/terminology/validation/TermCodeValidation.java
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/terminology/validation/TermCodeValidation.java
@@ -62,4 +62,46 @@ public List<TermCode> getInvalidTermCodes(StructuredQuery structuredQuery) {
 
     return invalidTermCodes;
   }
+
+  private Criterion removeFilters(Criterion in) {
+    return Criterion.builder()
+        .termCodes(in.termCodes())
+        .context(in.context())
+        .build();
+  }
+
+  public List<Criterion> getInvalidCriteria(StructuredQuery structuredQuery) {
+    var invalidCriteria = new ArrayList<Criterion>();
+
+    List<List<Criterion>> combinedCriteria;
+
+    if (structuredQuery.exclusionCriteria() != null && !structuredQuery.exclusionCriteria().isEmpty()) {
+      combinedCriteria = Stream.of(
+          structuredQuery.inclusionCriteria(),
+          structuredQuery.exclusionCriteria()).flatMap(
+          Collection::stream).toList();
+    } else {
+      combinedCriteria = structuredQuery.inclusionCriteria();
+    }
+
+    for (List<Criterion> criterionList : combinedCriteria) {
+      for (Criterion criterion : criterionList) {
+        if (criterion.context() == null) {
+          log.debug("Missing context");
+          invalidCriteria.add(removeFilters(criterion));
+        }
+        for (TermCode termCode : criterion.termCodes()) {
+          if (terminologyService.isExistingTermCode(termCode.system(), termCode.code(), termCode.version())) {
+            log.trace("termcode ok: {} - {} - {}", termCode.system(), termCode.code(), termCode.version());
+          } else {
+            log.debug("termcode invalid: {} - {} - {}", termCode.system(), termCode.code(),
+                termCode.version());
+            invalidCriteria.add(removeFilters(criterion));
+          }
+        }
+      }
+    }
+
+    return invalidCriteria;
+  }
 }
diff --git a/src/main/resources/static/v3/api-docs/swagger.yaml b/src/main/resources/static/v3/api-docs/swagger.yaml
index 98e88284..3790807d 100644
--- a/src/main/resources/static/v3/api-docs/swagger.yaml
+++ b/src/main/resources/static/v3/api-docs/swagger.yaml
@@ -109,6 +109,35 @@ paths:
       security:
         - feasibility_auth:
             - user
+  /query/validate:
+    post:
+      tags:
+        - query
+        - validation
+      summary: Validates a submitted (structured) query to check for schema violations or invalid termCodes
+      operationId: validateQuery
+      requestBody:
+        description: Structured query to validate
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/StructuredQuery'
+        required: true
+      responses:
+        200:
+          description: Query adheres to json schema. If invalid termCodes are present, they will be in the response.
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  $ref: '#/components/schemas/ValidatedStructuredQuery'
+        400:
+          description: Query does not adhere to json schema
+          content: { }
+        401:
+          description: Unauthorized - please login first
+          content: { }
   /query/by-user/{userId}:
     get:
       tags:
@@ -987,6 +1016,18 @@ components:
           type: array
           items:
             $ref: "#/components/schemas/CriterionList"
+    ValidatedStructuredQuery:
+      type: object
+      required:
+        - query
+        - invalidTerms
+      properties:
+        query:
+          $ref: "#/components/schemas/StructuredQuery"
+        invalidTerms:
+          type: array
+          items:
+            $ref: "#/components/schemas/TermCode"
     SavedQuery:
       type: object
       required:
diff --git a/src/test/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestControllerIT.java b/src/test/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestControllerIT.java
index 79dceaa0..5e9ddb12 100644
--- a/src/test/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestControllerIT.java
+++ b/src/test/java/de/numcodex/feasibility_gui_backend/query/v3/QueryHandlerRestControllerIT.java
@@ -184,7 +184,7 @@ public void testRunQueryEndpoint_FailsOnSoftQuotaExceeded() throws Exception {
 
     @Test
     @WithMockUser(roles = "FEASIBILITY_TEST_USER", username = "test")
-    public void testValidateQueryEndpoint_SucceedsOnValidQuery() throws Exception {
+    public void testValidate2QueryEndpoint_SucceedsOnValidQuery() throws Exception {
         StructuredQuery testQuery = createValidStructuredQuery();
 
         doReturn(List.of()).when(termCodeValidation).getInvalidTermCodes(any(StructuredQuery.class));
@@ -192,18 +192,28 @@ public void testValidateQueryEndpoint_SucceedsOnValidQuery() throws Exception {
         mockMvc.perform(post(URI.create(PATH_API + PATH_QUERY + "/validate")).with(csrf())
                 .contentType(APPLICATION_JSON)
                 .content(jsonUtil.writeValueAsString(testQuery)))
-            .andExpect(status().isNoContent());
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.invalidTerms").isEmpty());
     }
 
     @Test
     @WithMockUser(roles = "FEASIBILITY_TEST_USER")
-    public void testValidateQueryEndpoint_FailsOnInvalidStructuredQueryWith400() throws Exception {
-        var testQuery = StructuredQuery.builder().build();
+    public void testValidate2QueryEndpoint_SucceedsDespiteInvalidTermcodesWith200() throws Exception {
+        StructuredQuery testQuery = createValidStructuredQuery();
+        var invalidTermCode = TermCode.builder()
+            .code("LL2191-6")
+            .system("http://loinc.org")
+            .display("Geschlecht")
+            .build();
+
+        doReturn(List.of(invalidTermCode)).when(termCodeValidation).getInvalidTermCodes(any(StructuredQuery.class));
 
         mockMvc.perform(post(URI.create(PATH_API + PATH_QUERY + "/validate")).with(csrf())
                 .contentType(APPLICATION_JSON)
                 .content(jsonUtil.writeValueAsString(testQuery)))
-            .andExpect(status().isBadRequest());
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("$.invalidTerms").exists())
+            .andExpect(jsonPath("$.invalidTerms").isNotEmpty());
     }
 
     @Test