feat: Adds close_heapsnapshot MCP tool (#2174)

This commit adds the close_heapsnapshot MCP tool such that the coding
agent can close heap snapshots again.

Co-authored-by: Dominik Inführ <dinfuehr@chromium.org>
Co-authored-by: Nicholas Roscino <nroscino@google.com>

README.md

@@ -514,8 +514,9 @@ If you run into any issues, checkout our [troubleshooting guide](./docs/troubles
   - [`take_snapshot`](docs/tool-reference.md#take_snapshot)
   - [`screencast_start`](docs/tool-reference.md#screencast_start)
   - [`screencast_stop`](docs/tool-reference.md#screencast_stop)
-- **Memory** (5 tools)
+- **Memory** (6 tools)
   - [`take_heapsnapshot`](docs/tool-reference.md#take_heapsnapshot)
+  - [`close_heapsnapshot`](docs/tool-reference.md#close_heapsnapshot)
   - [`get_heapsnapshot_class_nodes`](docs/tool-reference.md#get_heapsnapshot_class_nodes)
   - [`get_heapsnapshot_details`](docs/tool-reference.md#get_heapsnapshot_details)
   - [`get_heapsnapshot_retainers`](docs/tool-reference.md#get_heapsnapshot_retainers)

docs/tool-reference.md

@@ -39,8 +39,9 @@
   - [`take_snapshot`](#take_snapshot)
   - [`screencast_start`](#screencast_start)
   - [`screencast_stop`](#screencast_stop)
-- **[Memory](#memory)** (5 tools)
+- **[Memory](#memory)** (6 tools)
   - [`take_heapsnapshot`](#take_heapsnapshot)
+  - [`close_heapsnapshot`](#close_heapsnapshot)
   - [`get_heapsnapshot_class_nodes`](#get_heapsnapshot_class_nodes)
   - [`get_heapsnapshot_details`](#get_heapsnapshot_details)
   - [`get_heapsnapshot_retainers`](#get_heapsnapshot_retainers)
@@ -454,6 +455,16 @@ in the DevTools Elements panel (if any).
 
 ---
 
+### `close_heapsnapshot`
+
+**Description:** Closes a previously loaded memory heapsnapshot, freeing its memory. (requires flag: --experimentalMemory=true)
+
+**Parameters:**
+
+- **filePath** (string) **(required)**: A path to the .heapsnapshot file to close.
+
+---
+
 ### `get_heapsnapshot_class_nodes`
 
 **Description:** Loads a memory heapsnapshot and returns instances of a specific class with their IDs. (requires flag: --experimentalMemory=true)

src/HeapSnapshotManager.ts

@@ -201,12 +201,18 @@ export class HeapSnapshotManager {
     return {snapshot, worker: workerProxy};
   }
 
-  dispose(filePath: string): void {
+  hasSnapshots(): boolean {
+    return this.#snapshots.size > 0;
+  }
+
+  dispose(filePath: string): boolean {
     const absolutePath = path.resolve(filePath);
     const cached = this.#snapshots.get(absolutePath);
     if (cached) {
       cached.worker.dispose();
       this.#snapshots.delete(absolutePath);
+      return true;
     }
+    return false;
   }
 }

src/McpContext.ts

@@ -889,4 +889,12 @@ export class McpContext implements Context {
   ): Promise<DevTools.HeapSnapshotModel.HeapSnapshotModel.ItemsRange> {
     return await this.#heapSnapshotManager.getRetainers(filePath, nodeId);
   }
+
+  async closeHeapSnapshot(filePath: string): Promise<boolean> {
+    return this.#heapSnapshotManager.dispose(filePath);
+  }
+
+  hasHeapSnapshots(): boolean {
+    return this.#heapSnapshotManager.hasSnapshots();
+  }
 }

src/bin/chrome-devtools-cli-options.ts

@@ -81,6 +81,19 @@ export const commands: Commands = {
       },
     },
   },
+  close_heapsnapshot: {
+    description:
+      'Closes a previously loaded memory heapsnapshot, freeing its memory. (requires flag: --experimentalMemory=true)',
+    category: 'Memory',
+    args: {
+      filePath: {
+        name: 'filePath',
+        type: 'string',
+        description: 'A path to the .heapsnapshot file to close.',
+        required: true,
+      },
+    },
+  },
   close_page: {
     description:
       'Closes the page by its index. The last open page cannot be closed.',

src/telemetry/tool_call_metrics.json

@@ -738,5 +738,14 @@
         "argType": "number"
       }
     ]
+  },
+  {
+    "name": "close_heapsnapshot",
+    "args": [
+      {
+        "name": "file_path_length",
+        "argType": "number"
+      }
+    ]
   }
 ]

src/tools/ToolDefinition.ts

@@ -248,6 +248,7 @@ export type Context = Readonly<{
     filePath: string,
     nodeId: number,
   ): Promise<DevTools.HeapSnapshotModel.HeapSnapshotModel.ItemsRange>;
+  closeHeapSnapshot(filePath: string): Promise<boolean>;
 }>;
 
 /**

src/tools/memory.ts

@@ -154,3 +154,32 @@ export const getHeapSnapshotRetainers = defineTool({
     });
   },
 });
+
+export const closeHeapSnapshot = defineTool({
+  name: 'close_heapsnapshot',
+  description:
+    'Closes a previously loaded memory heapsnapshot, freeing its memory.',
+  annotations: {
+    category: ToolCategory.MEMORY,
+    readOnlyHint: false,
+    conditions: ['experimentalMemory'],
+  },
+  verifyFilesSchema: ['filePath'],
+  schema: {
+    filePath: zod
+      .string()
+      .describe('A path to the .heapsnapshot file to close.'),
+  },
+  blockedByDialog: false,
+  handler: async (request, response, context) => {
+    const closed = await context.closeHeapSnapshot(request.params.filePath);
+    if (!closed) {
+      throw new Error(
+        `Failed to close heap snapshot: ${request.params.filePath} was not loaded.`,
+      );
+    }
+    response.appendResponseLine(
+      `Closed heap snapshot: ${request.params.filePath}`,
+    );
+  },
+});

tests/tools/memory.test.ts

@@ -17,6 +17,7 @@ import {
   getHeapSnapshotDetails,
   getHeapSnapshotClassNodes,
   getHeapSnapshotRetainers,
+  closeHeapSnapshot,
 } from '../../src/tools/memory.js';
 import {withMcpContext} from '../utils.js';
 
@@ -176,4 +177,50 @@ describe('memory', () => {
       });
     });
   });
+
+  describe('close_heapsnapshot', () => {
+    it('with default options', async () => {
+      await withMcpContext(async (response, context) => {
+        const filePath = join(
+          process.cwd(),
+          'tests/fixtures/example.heapsnapshot',
+        );
+
+        await getHeapSnapshotSummary.handler(
+          {params: {filePath}},
+          response,
+          context,
+        );
+
+        assert.ok(context.hasHeapSnapshots());
+
+        await closeHeapSnapshot.handler(
+          {params: {filePath}},
+          response,
+          context,
+        );
+
+        assert.ok(
+          response.responseLines.includes(`Closed heap snapshot: ${filePath}`),
+        );
+        assert.ok(!context.hasHeapSnapshots());
+      });
+    });
+
+    it('with non-existent snapshot', async () => {
+      await withMcpContext(async (response, context) => {
+        const filePath = join(
+          process.cwd(),
+          'tests/fixtures/example.heapsnapshot',
+        );
+
+        await assert.rejects(
+          closeHeapSnapshot.handler({params: {filePath}}, response, context),
+          {
+            message: `Failed to close heap snapshot: ${filePath} was not loaded.`,
+          },
+        );
+      });
+    });
+  });
 });