diff --git a/docling-serve/docling-serve-api/src/main/java/ai/docling/serve/api/validation/ValidationErrorDetail.java b/docling-serve/docling-serve-api/src/main/java/ai/docling/serve/api/validation/ValidationErrorDetail.java
index 0c9b1d55..e63e7a2f 100644
--- a/docling-serve/docling-serve-api/src/main/java/ai/docling/serve/api/validation/ValidationErrorDetail.java
+++ b/docling-serve/docling-serve-api/src/main/java/ai/docling/serve/api/validation/ValidationErrorDetail.java
@@ -62,7 +62,7 @@ public class ValidationErrorDetail {
    */
   @JsonProperty("input")
   @Nullable
-  private String input;
+  private Object input;
 
   /**
    * Represents the context information associated with a validation error.
diff --git a/docling-serve/docling-serve-client/src/test/java/ai/docling/serve/client/ValidationErrorDeserializationTests.java b/docling-serve/docling-serve-client/src/test/java/ai/docling/serve/client/ValidationErrorDeserializationTests.java
new file mode 100644
index 00000000..0953b908
--- /dev/null
+++ b/docling-serve/docling-serve-client/src/test/java/ai/docling/serve/client/ValidationErrorDeserializationTests.java
@@ -0,0 +1,146 @@
+package ai.docling.serve.client;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+import ai.docling.serve.api.validation.ValidationError;
+import ai.docling.serve.api.validation.ValidationErrorDetail;
+
+class ValidationErrorDeserializationTests {
+  private final JsonMapper jsonMapper = JsonMapper.builder()
+      .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
+      .build();
+
+  @Test
+  void deserializeWithStringInput() throws Exception {
+    var json = """
+        {
+          "detail": [{
+            "type": "url_scheme",
+            "loc": ["body", "sources", 0, "http", "url"],
+            "msg": "URL scheme should be 'http' or 'https'",
+            "input": "file:///path/to/file.pdf"
+          }]
+        }
+        """;
+
+    var error = jsonMapper.readValue(json, ValidationError.class);
+
+    assertThat(error.getErrorDetails())
+        .singleElement()
+        .satisfies(detail -> {
+          assertThat(detail.getType()).isEqualTo("url_scheme");
+          assertThat(detail.getMessage()).isEqualTo("URL scheme should be 'http' or 'https'");
+          assertThat(detail.getLocations()).isEqualTo(List.of("body", "sources", 0, "http", "url"));
+          assertThat(detail.getInput()).isEqualTo("file:///path/to/file.pdf");
+        });
+  }
+
+  @Test
+  void deserializeWithObjectInput() throws Exception {
+    var json = """
+        {
+          "detail": [{
+            "type": "missing",
+            "loc": ["body", "sources", 0, "file", "base64_string"],
+            "msg": "Field required",
+            "input": {"kind": "file"}
+          }]
+        }
+        """;
+
+    var error = jsonMapper.readValue(json, ValidationError.class);
+
+    assertThat(error.getErrorDetails())
+        .singleElement()
+        .satisfies(detail -> {
+          assertThat(detail.getType()).isEqualTo("missing");
+          assertThat(detail.getMessage()).isEqualTo("Field required");
+          assertThat(detail.getLocations()).isEqualTo(List.of("body", "sources", 0, "file", "base64_string"));
+          assertThat(detail.getInput())
+              .isInstanceOf(Map.class)
+              .isEqualTo(Map.of("kind", "file"));
+        });
+  }
+
+  @Test
+  void deserializeWithNullInput() throws Exception {
+    var json = """
+        {
+          "detail": [{
+            "type": "value_error",
+            "loc": ["body"],
+            "msg": "Value error"
+          }]
+        }
+        """;
+
+    var error = jsonMapper.readValue(json, ValidationError.class);
+
+    assertThat(error.getErrorDetails())
+        .singleElement()
+        .satisfies(detail -> {
+          assertThat(detail.getType()).isEqualTo("value_error");
+          assertThat(detail.getInput()).isNull();
+        });
+  }
+
+  @Test
+  void deserializeMultipleErrorDetails() throws Exception {
+    var json = """
+        {
+          "detail": [
+            {
+              "type": "missing",
+              "loc": ["body", "sources", 0, "file", "base64_string"],
+              "msg": "Field required",
+              "input": {"kind": "file"}
+            },
+            {
+              "type": "missing",
+              "loc": ["body", "sources", 0, "file", "filename"],
+              "msg": "Field required",
+              "input": {"kind": "file"}
+            }
+          ]
+        }
+        """;
+
+    var error = jsonMapper.readValue(json, ValidationError.class);
+
+    assertThat(error.getErrorDetails()).hasSize(2);
+    assertThat(error.getErrorDetails())
+        .extracting(ValidationErrorDetail::getMessage)
+        .containsOnly("Field required");
+    assertThat(error.getErrorDetails())
+        .extracting(ValidationErrorDetail::getInput)
+        .allSatisfy(input -> assertThat(input).isEqualTo(Map.of("kind", "file")));
+  }
+
+  @Test
+  void builderAcceptsStringInput() {
+    var detail = ValidationErrorDetail.builder()
+        .type("url_scheme")
+        .input("file:///path/to/file.pdf")
+        .build();
+
+    assertThat(detail.getInput()).isEqualTo("file:///path/to/file.pdf");
+  }
+
+  @Test
+  void builderAcceptsObjectInput() {
+    var detail = ValidationErrorDetail.builder()
+        .type("missing")
+        .input(Map.of("kind", "file"))
+        .build();
+
+    assertThat(detail.getInput()).isEqualTo(Map.of("kind", "file"));
+  }
+}