diff --git a/src/builtins.ts b/src/builtins.ts
index 070ed52..eb09b99 100644
--- a/src/builtins.ts
+++ b/src/builtins.ts
@@ -23,6 +23,7 @@ export const BUILTIN_TOOLS: ReadonlySet<string> = new Set([
   "Read",
   "ReadNotifications",
   "RemoteTrigger",
+  "ReportFindings",
   "ScheduleWakeup",
   "SendMessage",
   "SendUserFile",
diff --git a/test/builtins.test.ts b/test/builtins.test.ts
index b27a445..98b31b4 100644
--- a/test/builtins.test.ts
+++ b/test/builtins.test.ts
@@ -32,6 +32,10 @@ describe("builtins", () => {
     expect(BUILTIN_TOOLS.has("Workflow")).toBe(true);
   });
 
+  it("BUILTIN_TOOLS includes ReportFindings", () => {
+    expect(BUILTIN_TOOLS.has("ReportFindings")).toBe(true);
+  });
+
   it("isMcpTool detects mcp__ prefix", () => {
     expect(isMcpTool("mcp__github__create_issue")).toBe(true);
     expect(isMcpTool("Read")).toBe(false);
diff --git a/test/checks.test.ts b/test/checks.test.ts
index e4bf45c..480835e 100644
--- a/test/checks.test.ts
+++ b/test/checks.test.ts
@@ -1185,6 +1185,16 @@ describe("runChecks", () => {
     const ds = runChecks([s], config);
     expect(ds.find((d) => d.rule === "tool-unknown")).toBeUndefined();
   });
+
+  it("does not flag ReportFindings as an unknown tool", () => {
+    const s = mkSkill("/test/foo/SKILL.md", {
+      name: "foo",
+      description: "do the foo thing",
+      "allowed-tools": "ReportFindings Read",
+    });
+    const ds = runChecks([s], config);
+    expect(ds.find((d) => d.rule === "tool-unknown")).toBeUndefined();
+  });
 });
 
 describe("buildValidated", () => {