Add option to encode structuredContent as TOON

Author: Piotr Paulski

package-lock.json

@@ -54,6 +54,7 @@
     "@rollup/plugin-json": "^6.1.0",
     "@rollup/plugin-node-resolve": "^16.0.3",
     "@stylistic/eslint-plugin": "^5.4.0",
+    "@toon-format/toon": "^2.2.0",
     "@types/debug": "^4.1.12",
     "@types/filesystem": "^0.0.36",
     "@types/node": "^25.0.0",

package.json

@@ -13,6 +13,7 @@ import {SlimMcpResponse} from './SlimMcpResponse.js';
 import {ClearcutLogger} from './telemetry/ClearcutLogger.js';
 import {bucketizeLatency} from './telemetry/metricUtils.js';
 import type {CallToolResult, zod} from './third_party/index.js';
+import {toonEncode} from './third_party/index.js';
 import type {ToolCategory} from './tools/categories.js';
 import {labels, OFF_BY_DEFAULT_CATEGORIES} from './tools/categories.js';
 import type {DefinedPageTool, ToolDefinition} from './tools/ToolDefinition.js';
@@ -221,7 +222,11 @@ export class ToolHandler {
       }
       success = true;
       if (this.serverArgs.experimentalStructuredContent) {
-        result.structuredContent = structuredContent as Record<string, unknown>;
+        if (this.serverArgs.experimentalStructuredContentFormat === 'toon') {
+          result.structuredContent = { toon: toonEncode(structuredContent)};
+        } else {
+          result.structuredContent = structuredContent as Record<string, unknown>;
+        }
       }
       return result;
     } catch (err) {

src/ToolHandler.ts

@@ -174,6 +174,12 @@ export const cliOptions = {
     describe: 'Whether to output structured formatted content.',
     hidden: true,
   },
+  experimentalStructuredContentFormat: {
+    type: 'string',
+    describe: 'The format of the structured content. Defaults to "json".',
+    choices: ['toon', 'json'] as const,
+    hidden: true,
+  },
   experimentalIncludeAllPages: {
     type: 'boolean',
     describe:
@@ -299,7 +305,7 @@ export function parseArguments(
   const yargsInstance = yargs(hideBin(argv))
     .scriptName('npx chrome-devtools-mcp@latest')
     .options(cliOptions)
-    .check(args => {
+    .middleware(args => {
       // We can't set default in the options else
       // Yargs will complain
       if (
@@ -316,6 +322,19 @@ export function parseArguments(
         );
         args.usageStatistics = false;
       }
+      if (args.experimentalStructuredContentFormat && args.experimentalStructuredContent === undefined) {
+        args.experimentalStructuredContent = true;
+      }
+      if (args.experimentalStructuredContentFormat === undefined && args.experimentalStructuredContent) {
+        args.experimentalStructuredContentFormat = 'json';
+      }
+    })
+    .check(args => {
+      if (args.experimentalStructuredContentFormat && !args.experimentalStructuredContent) {
+        throw new Error(
+          'The --experimentalStructuredContentFormat option can only be used when --experimentalStructuredContent is enabled.'
+        );
+      }
       return true;
     })
     .example([

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

@@ -54,6 +54,7 @@ export {
   Browser as BrowserEnum,
   type ChromeReleaseChannel as BrowsersChromeReleaseChannel,
 } from '@puppeteer/browsers';
+export {encode as toonEncode} from '@toon-format/toon';
 
 import {
   snapshot as snapshotImpl,