diff --git a/scripts/update_tool_call_metrics.ts b/scripts/update_tool_call_metrics.ts
index bbf017f4c..f28e2688d 100644
--- a/scripts/update_tool_call_metrics.ts
+++ b/scripts/update_tool_call_metrics.ts
@@ -8,7 +8,11 @@ import * as fs from 'node:fs';
 import * as path from 'node:path';
 
 import type {ParsedArguments} from '../build/src/bin/chrome-devtools-mcp-cli-options.js';
-import {generateToolMetrics} from '../build/src/telemetry/toolMetricsUtils.js';
+import {
+  applyToExistingMetrics,
+  generateToolMetrics,
+  type ToolMetric,
+} from '../build/src/telemetry/toolMetricsUtils.js';
 import type {ToolDefinition} from '../build/src/tools/ToolDefinition.js';
 import {createTools} from '../build/src/tools/tools.js';
 
@@ -35,16 +39,26 @@ function writeToolCallMetricsConfig() {
     throw new Error('Error: Duplicate tool names found.');
   }
 
-  // Map tools to their metadata
-  const toolData = generateToolMetrics(allTools);
+  let existingMetrics: ToolMetric[] = [];
+  if (fs.existsSync(outputPath)) {
+    try {
+      existingMetrics = JSON.parse(
+        fs.readFileSync(outputPath, 'utf8'),
+      ) as ToolMetric[];
+    } catch {
+      console.warn(
+        `Warning: Failed to parse existing metrics from ${outputPath}. Starting fresh.`,
+      );
+    }
+  }
 
-  // Sort by name for determinism
-  toolData.sort((a, b) => a.name.localeCompare(b.name));
+  const newMetrics = generateToolMetrics(allTools);
+  const mergedMetrics = applyToExistingMetrics(existingMetrics, newMetrics);
 
-  fs.writeFileSync(outputPath, JSON.stringify(toolData, null, 2) + '\n');
+  fs.writeFileSync(outputPath, JSON.stringify(mergedMetrics, null, 2) + '\n');
 
   console.log(
-    `Successfully wrote ${toolData.length} tool names with arguments to ${outputPath}`,
+    `Successfully wrote ${mergedMetrics.length} total tool metrics (including deprecated ones) to ${outputPath}`,
   );
 }
 
diff --git a/src/telemetry/toolMetricsUtils.ts b/src/telemetry/toolMetricsUtils.ts
index 124913a68..30ba81b53 100644
--- a/src/telemetry/toolMetricsUtils.ts
+++ b/src/telemetry/toolMetricsUtils.ts
@@ -30,11 +30,61 @@ export function validateEnumHomogeneity(values: unknown[]): string {
 export interface ArgMetric {
   name: string;
   argType: string;
+  isDeprecated?: boolean;
 }
 
 export interface ToolMetric {
   name: string;
   args: ArgMetric[];
+  isDeprecated?: boolean;
+}
+
+export function applyToExistingMetrics(
+  existing: ToolMetric[],
+  update: ToolMetric[],
+): ToolMetric[] {
+  const updated = applyToExisting<ToolMetric>(existing, update);
+  const existingByName = new Map(existing.map(tool => [tool.name, tool]));
+  const updatedByName = new Map(update.map(tool => [tool.name, tool]));
+
+  return updated.map(tool => {
+    const existingTool = existingByName.get(tool.name);
+    const updatedTool = updatedByName.get(tool.name);
+    // If the tool still exists in the update, we will update the args.
+    if (existingTool && updatedTool) {
+      const updatedArgs = applyToExisting<ArgMetric>(
+        existingTool.args,
+        updatedTool.args,
+      );
+      return {...tool, args: updatedArgs};
+    }
+    return tool;
+  });
+}
+
+function applyToExisting<T extends {name: string; isDeprecated?: boolean}>(
+  existing: T[],
+  update: T[],
+): T[] {
+  const existingNames = new Set(existing.map(item => item.name));
+  const updatedNames = new Set(update.map(item => item.name));
+
+  const result: T[] = [];
+  // Keep the original ordering.
+  for (const entry of existing) {
+    const toAdd = {...entry};
+    if (!updatedNames.has(entry.name)) {
+      toAdd.isDeprecated = true;
+    }
+    result.push(toAdd);
+  }
+  // New entries must be added to the very back of the list.
+  for (const entry of update) {
+    if (!existingNames.has(entry.name)) {
+      result.push({...entry});
+    }
+  }
+  return result;
 }
 
 /**
diff --git a/tests/telemetry/toolMetricsUtils.test.ts b/tests/telemetry/toolMetricsUtils.test.ts
index a984c4287..0c369aaea 100644
--- a/tests/telemetry/toolMetricsUtils.test.ts
+++ b/tests/telemetry/toolMetricsUtils.test.ts
@@ -8,6 +8,7 @@ import assert from 'node:assert';
 import {describe, it} from 'node:test';
 
 import {
+  applyToExistingMetrics,
   generateToolMetrics,
   validateEnumHomogeneity,
 } from '../../src/telemetry/toolMetricsUtils.js';
@@ -80,4 +81,183 @@ describe('toolMetricsUtils', () => {
       assert.strictEqual(metrics[0].args[0].argType, 'string');
     });
   });
+
+  describe('applyToExistingMetrics', () => {
+    it('should return the same metrics if existing and update are the same', () => {
+      const existing = [{name: 'foo', args: []}];
+      const update = [{name: 'foo', args: []}];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [{name: 'foo', args: []}];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should append new entries to the end of the array', () => {
+      const existing = [{name: 'foo', args: []}];
+      const update = [
+        {name: 'foo', args: []},
+        {name: 'bar', args: []},
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {name: 'foo', args: []},
+        {name: 'bar', args: []},
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should mark missing entries as deprecated and preserve their order', () => {
+      const existing = [
+        {name: 'foo', args: []},
+        {name: 'bar', args: []},
+      ];
+      const update = [{name: 'foo', args: []}];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {name: 'foo', args: []},
+        {name: 'bar', args: [], isDeprecated: true},
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should handle adding new entries and deprecating old ones simultaneously', () => {
+      const existing = [
+        {name: 'foo', args: []},
+        {name: 'bar', args: []},
+      ];
+      const update = [
+        {name: 'bar', args: []},
+        {name: 'baz', args: []},
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {name: 'foo', args: [], isDeprecated: true},
+        {name: 'bar', args: []},
+        {name: 'baz', args: []},
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should append new arguments to the back', () => {
+      const existing = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+      ];
+      const update = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string'},
+            {name: 'arg_b', argType: 'string'},
+          ],
+        },
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string'},
+            {name: 'arg_b', argType: 'string'},
+          ],
+        },
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should mark removed arguments as deprecated', () => {
+      const existing = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string'},
+            {name: 'arg_b', argType: 'string'},
+          ],
+        },
+      ];
+      const update = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string'},
+            {name: 'arg_b', argType: 'string', isDeprecated: true},
+          ],
+        },
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should not change args if they are the same', () => {
+      const existing = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+      ];
+      const update = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should handle adding and removing arguments simultaneously', () => {
+      const existing = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string'},
+            {name: 'arg_b', argType: 'string'},
+          ],
+        },
+      ];
+      const update = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_b', argType: 'string'},
+            {name: 'arg_c', argType: 'string'},
+          ],
+        },
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string', isDeprecated: true},
+            {name: 'arg_b', argType: 'string'},
+            {name: 'arg_c', argType: 'string'},
+          ],
+        },
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+
+    it('should handle tool and argument changes simultaneously', () => {
+      const existing = [
+        {name: 'foo', args: [{name: 'arg_a', argType: 'string'}]},
+        {name: 'bar', args: []},
+      ];
+      const update = [
+        {name: 'foo', args: [{name: 'arg_b', argType: 'string'}]},
+        {name: 'baz', args: []},
+      ];
+      const result = applyToExistingMetrics(existing, update);
+      const expected = [
+        {
+          name: 'foo',
+          args: [
+            {name: 'arg_a', argType: 'string', isDeprecated: true},
+            {name: 'arg_b', argType: 'string'},
+          ],
+        },
+        {name: 'bar', args: [], isDeprecated: true},
+        {name: 'baz', args: []},
+      ];
+      assert.deepStrictEqual(result, expected);
+    });
+  });
 });