diff --git a/src/test/java/com/babelqueue/kafka/EnvelopeShapeTest.java b/src/test/java/com/babelqueue/kafka/EnvelopeShapeTest.java
new file mode 100644
index 0000000..c27db0e
--- /dev/null
+++ b/src/test/java/com/babelqueue/kafka/EnvelopeShapeTest.java
@@ -0,0 +1,92 @@
+package com.babelqueue.kafka;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.babelqueue.BabelQueueException;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Direct accept/reject table for {@link EnvelopeShape} (the poison trigger set, broker-bindings.md section 6.5):
+ * the JSON lexer paths (numbers, string escapes, literals, nesting) that the shared conformance vectors exercise only
+ * partially.
+ */
+class EnvelopeShapeTest {
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+        "{}",
+        "null",
+        "  {\"trace_id\":null,\"attempts\":null,\"meta\":null,\"data\":null,\"dead_letter\":null}  ",
+        "{\"unknown\":[]}",
+        "{\"unknown\":{\"a\":[1,{\"b\":null}]}}",
+        "{\"data\":{\"n\":0,\"m\":-0.5E-2,\"k\":12.5e+3,\"z\":-7,\"t\":true,\"f\":false,\"u\":null}}",
+        "{\"data\":{\"s\":\"q\\\" \\\\ \\/ \\b \\f \\n \\r \\t \\u00e9 \\u0041\",\"a\":[1,[2],[]],\"o\":{}}}",
+        "{\"meta\":{\"id\":\"x\",\"queue\":null,\"lang\":\"go\",\"schema_version\":1,\"created_at\":1700000000}}",
+        "{\"dead_letter\":{\"reason\":\"r\",\"failed_at\":1,\"attempts\":null,\"original_queue\":\"q\"}}",
+        "{\"meta\":{\"unknown\":[1,2,3]}}",
+    })
+    void acceptsWellFormedTypedBodies(String body) {
+        assertNull(EnvelopeShape.violation(body), body);
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+        "",
+        "   ",
+        "[1]",
+        "7",
+        "{} trailing",
+        "{",
+        "{\"a\"",
+        "{1:2}",
+        "{\"a\" 1}",
+        "{\"a\":1 \"b\":2}",
+        "{\"a\":}",
+        "{\"unknown\":?}",
+        "{\"unknown\":tru}",
+        "{\"unknown\":nul}",
+        "{\"data\":{\"n\":01}}",
+        "{\"data\":{\"n\":-}}",
+        "{\"data\":{\"n\":1.}}",
+        "{\"data\":{\"n\":1e}}",
+        "{\"data\":{\"n\":1e+}}",
+        "{\"data\":{\"n\":1e999}}",
+        "{\"data\":{\"a\":[1 2]}}",
+        "{\"data\":{\"a\":[1,2}}}",
+        "{\"data\":{\"a\":{\"b\":1 \"c\":2}}}",
+        "{\"data\":{\"a\":{1:2}}}",
+        "{\"data\":[1]}",
+        "{\"data\":\"x\"}",
+        "{\"meta\":[1]}",
+        "{\"meta\":{\"id\":1}}",
+        "{\"meta\":{\"schema_version\":\"1\"}}",
+        "{\"meta\":{\"created_at\":1.5}}",
+        "{\"dead_letter\":{\"attempts\":1e2}}",
+        "{\"attempts\":99999999999999999999}",
+        "{\"attempts\":\"x\"}",
+        "{\"attempts\":1.5}",
+        "{\"trace_id\":5}",
+        "{\"unknown\":\"abc",
+        "{\"unknown\":\"\\",
+        "{\"unknown\":\"\\q\"}",
+        "{\"unknown\":\"\\u12\"}",
+        "{\"unknown\":\"\\u12zz\"}",
+        "{\"unknown\":\"\\u00",
+        "{\"unknown\":\"a\tb\"}",
+    })
+    void rejectsMalformedOrMistypedBodies(String body) {
+        BabelQueueException violation = EnvelopeShape.violation(body);
+        assertNotNull(violation, body);
+        assertTrue(violation.getMessage().startsWith("Undecodable BabelQueue body: "), violation.getMessage());
+    }
+
+    @Test
+    void rejectsNestingBeyondTheLimitWithoutThrowing() {
+        String body = "{\"data\":" + "[".repeat(20_000) + "]".repeat(20_000) + "}";
+        assertNotNull(EnvelopeShape.violation(body));
+    }
+}