diff --git a/src/main/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputs.java b/src/main/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputs.java
index f7d10a2..7ff5e7b 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputs.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputs.java
@@ -8,6 +8,7 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
+import it.cnr.isti.workflow.manager.executions.NodeExecutionException;
 import it.cnr.isti.workflow.manager.blocks.configurations.LLMOutputField;
 import tools.jackson.core.JacksonException;
 import tools.jackson.databind.JsonNode;
@@ -30,9 +31,34 @@ final class StructuredLLMOutputs {
 
     private static final ObjectMapper MAPPER = new ObjectMapper();
 
+    /** The step's error code when the answer does not carry the fields the node declared. */
+    static final String OUTPUT_MISSING = "LLM_STRUCTURED_OUTPUT_MISSING";
+
+    /**
+     * How much of the model's own words a failure quotes: enough to see what it did instead,
+     * not so much that the error drowns the message it belongs to.
+     */
+    private static final int QUOTED_CHARS = 600;
+
     private StructuredLLMOutputs() {
     }
 
+    /**
+     * The end of the reply, where the object was asked to be - and so where a model that wrote
+     * something else instead shows what that was.
+     */
+    private static String tail(String response) {
+        if (response == null || response.isBlank()) {
+            return "(nothing)";
+        }
+        String text = response.strip();
+        return text.length() <= QUOTED_CHARS ? text : "..." + text.substring(text.length() - QUOTED_CHARS);
+    }
+
+    private static String head(String text) {
+        return text.length() <= QUOTED_CHARS ? text : text.substring(0, QUOTED_CHARS) + "...";
+    }
+
     /**
      * The instruction appended to the prompt. Deliberately at the end and deliberately explicit
      * about "nothing after it": a model that keeps talking past the object makes the closing brace
@@ -67,14 +93,15 @@ final class StructuredLLMOutputs {
 
         JsonNode object = lastJsonObjectIn(response);
         if (object == null) {
-            throw new IllegalStateException("The model was asked to end its reply with a JSON object holding "
-                    + names(fields) + ", and did not. Its answer is on the response port, unchanged.");
+            throw new NodeExecutionException(OUTPUT_MISSING, "The model was asked to end its reply with a JSON"
+                    + " object holding " + names(fields) + ", and did not. Its reply ended: " + tail(response));
         }
         for (LLMOutputField field : fields) {
             JsonNode value = object.get(field.name());
             if (value == null || value.isNull()) {
-                throw new IllegalStateException("The model's closing JSON object has no \"" + field.name()
-                        + "\". It was asked for " + names(fields) + ".");
+                throw new NodeExecutionException(OUTPUT_MISSING, "The model's closing JSON object has no \""
+                        + field.name() + "\". It was asked for " + names(fields) + ". The object it wrote: "
+                        + head(object.toString()));
             }
             // A model asked for a string sometimes answers with a number or a nested object. Its
             // text form is what a port carries, so take that rather than refusing over a type.
diff --git a/src/test/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputsTest.java b/src/test/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputsTest.java
index 661e4db..66ffc69 100644
--- a/src/test/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputsTest.java
+++ b/src/test/java/it/cnr/isti/workflow/manager/executions/executors/blocks/StructuredLLMOutputsTest.java
@@ -13,6 +13,7 @@ import java.util.Map;
 
 import org.junit.jupiter.api.Test;
 
+import it.cnr.isti.workflow.manager.executions.NodeExecutionException;
 import it.cnr.isti.workflow.manager.blocks.configurations.LLMOutputField;
 
 /** Reading declared fields out of an answer a model wrote, including the ways it writes them badly. */
@@ -82,23 +83,38 @@ class StructuredLLMOutputsTest {
     void refusesAnAnswerWithNoObjectAtAll() {
         // The alternative is handing the flow empty ports, which everything downstream would treat
         // as an answer rather than as an absence.
-        IllegalStateException failure = assertThrows(IllegalStateException.class,
+        NodeExecutionException failure = assertThrows(NodeExecutionException.class,
                 () -> StructuredLLMOutputs.split("I could not manage it.", FIELDS, "response"));
 
+        assertEquals(StructuredLLMOutputs.OUTPUT_MISSING, failure.getErrorCode());
         assertTrue(failure.getMessage().contains("previewUrl, report"), failure.getMessage());
+        // The failed step publishes no ports, so the reply is only ever seen here.
+        assertTrue(failure.getMessage().endsWith("Its reply ended: I could not manage it."), failure.getMessage());
+    }
+
+    @Test
+    void quotesOnlyTheEndOfALongReplyWhereTheObjectShouldHaveBeen() {
+        String longReply = "x".repeat(5_000) + " and so the page is ready.";
+
+        NodeExecutionException failure = assertThrows(NodeExecutionException.class,
+                () -> StructuredLLMOutputs.split(longReply, FIELDS, "response"));
+
+        assertTrue(failure.getMessage().endsWith("and so the page is ready."), failure.getMessage());
+        assertTrue(failure.getMessage().length() < 1_000, "quoted, not dumped: " + failure.getMessage().length());
     }
 
     @Test
     void namesTheFieldTheModelLeftOut() {
-        IllegalStateException failure = assertThrows(IllegalStateException.class,
+        NodeExecutionException failure = assertThrows(NodeExecutionException.class,
                 () -> StructuredLLMOutputs.split("{\"previewUrl\": \"u\"}", FIELDS, "response"));
 
         assertTrue(failure.getMessage().contains("\"report\""), failure.getMessage());
+        assertTrue(failure.getMessage().endsWith("The object it wrote: {\"previewUrl\":\"u\"}"), failure.getMessage());
     }
 
     @Test
     void refusesANullFieldRatherThanPassingItOnAsEmpty() {
-        assertThrows(IllegalStateException.class,
+        assertThrows(NodeExecutionException.class,
                 () -> StructuredLLMOutputs.split("{\"previewUrl\": \"u\", \"report\": null}", FIELDS, "response"));
     }