diff --git a/packages/core/src/webmcp/types.ts b/packages/core/src/webmcp/types.ts
index 49f8d733257..cd6e24bdc4e 100644
--- a/packages/core/src/webmcp/types.ts
+++ b/packages/core/src/webmcp/types.ts
@@ -75,6 +75,12 @@ export interface Annotations {
    * author of the tool.
    */
   untrustedContentHint?: boolean;
+
+  /**
+   * A hint that the tool will have consequential effects like mutating state or interacting
+   * with the external world.
+   */
+  consequentialHint?: boolean;
 }
 
 /**
diff --git a/packages/core/test/webmcp/declare_tool_spec.ts b/packages/core/test/webmcp/declare_tool_spec.ts
index 93ea05288f7..488cceab1d8 100644
--- a/packages/core/test/webmcp/declare_tool_spec.ts
+++ b/packages/core/test/webmcp/declare_tool_spec.ts
@@ -79,6 +79,7 @@ describe('declareExperimentalWebMcpTool', () => {
         annotations: {
           readOnlyHint: true,
           untrustedContentHint: true,
+          consequentialHint: true,
         },
       },
       Injector.create({providers: []}),
@@ -89,6 +90,7 @@ describe('declareExperimentalWebMcpTool', () => {
         annotations: {
           readOnlyHint: true,
           untrustedContentHint: true,
+          consequentialHint: true,
         },
       }),
       jasmine.anything(),