From c566e33793a1c66feedde887a46916a5a00fea4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E2=80=9CSebastian?=
 <64795732+slegarraga@users.noreply.github.com>
Date: Thu, 6 Aug 2026 05:20:06 -0400
Subject: [PATCH] fix: guard invalid json schema patterns

---
 src/scorers/json-schema.ts | 10 ++++++++--
 tests/scorers.test.ts      |  9 +++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/scorers/json-schema.ts b/src/scorers/json-schema.ts
index c299302..d59fd80 100644
--- a/src/scorers/json-schema.ts
+++ b/src/scorers/json-schema.ts
@@ -56,8 +56,14 @@ export function validate(value: unknown, schema: JsonSchema, path = "$"): string
       errors.push(`${path}: shorter than minLength ${schema.minLength}`);
     if (schema.maxLength !== undefined && value.length > schema.maxLength)
       errors.push(`${path}: longer than maxLength ${schema.maxLength}`);
-    if (schema.pattern && !new RegExp(schema.pattern).test(value))
-      errors.push(`${path}: does not match pattern ${schema.pattern}`);
+    if (schema.pattern) {
+      try {
+        if (!new RegExp(schema.pattern).test(value))
+          errors.push(`${path}: does not match pattern ${schema.pattern}`);
+      } catch (err) {
+        errors.push(`${path}: invalid pattern ${schema.pattern}: ${(err as Error).message}`);
+      }
+    }
   }
 
   if (isPlainObject(value)) {
diff --git a/tests/scorers.test.ts b/tests/scorers.test.ts
index b53c6a2..1cdcb6d 100644
--- a/tests/scorers.test.ts
+++ b/tests/scorers.test.ts
@@ -107,6 +107,15 @@ describe("json-schema", () => {
     );
     expect(errs.length).toBe(2);
   });
+  it("fails cleanly when a schema pattern is invalid", async () => {
+    const r = await run(
+      jsonSchemaScorer,
+      { type: "json-schema", schema: { type: "string", pattern: "[a-z" } },
+      ctx('"abc"'),
+    );
+    expect(r.passed).toBe(false);
+    expect(r.reason).toContain("invalid pattern");
+  });
 });
 
 describe("embedding-similarity", () => {