fix: return message when page exposes no 3p developer tools - #3197

## Summary

Add a **Pre-submit checklist** section to `AGENTS.md`. Each item comes
from a recent review finding or a landed bug fix in this repository.

The checklist has five groups:

- **Scope and PR description**: one change per PR, title and commit type
match, description lists every behavior change and matches the diff,
`npm run gen` and `npm run format` ran.
- **Design**: fix in the lowest layer that owns the data, fix upstream
(Puppeteer, devtools-frontend) first, one helper for repeated code,
options objects instead of positional `undefined` arguments, validation
in Zod schemas.
- **Correctness and edge cases**: no stale state after a failed call,
artifacts written before a throw, abandoned async continuations, mutex
guards, file removal races, `dispose()` releases every resource, secrets
never reach logs, path parameters validated even when they parse as
URLs.
- **Tests**: every new function has a test, no vacuous assertions,
`notCalled` targets the first call after validation, exact-argument
assertions, reusable stubs in `tests/mocks.ts`, bounded timeouts, no
second CDP session for event waits.
- **Documentation and output**: tool descriptions state when a parameter
is ignored, skills stay generic, one-sentence inline comments.

Sources: review comments on ChromeDevTools#2679, ChromeDevTools#2797, ChromeDevTools#2859, ChromeDevTools#2881, ChromeDevTools#2901, ChromeDevTools#3048,
ChromeDevTools#3082, ChromeDevTools#3109, ChromeDevTools#3120, ChromeDevTools#3132, ChromeDevTools#3134, ChromeDevTools#3139, ChromeDevTools#3148, ChromeDevTools#3156, ChromeDevTools#3158, ChromeDevTools#3161,
ChromeDevTools#3182, ChromeDevTools#3183, ChromeDevTools#3186, ChromeDevTools#3187, ChromeDevTools#3188, ChromeDevTools#3189, ChromeDevTools#3192, ChromeDevTools#3196, ChromeDevTools#3197, ChromeDevTools#3198,
ChromeDevTools#3203, ChromeDevTools#3204, and fixes ChromeDevTools#3150, ChromeDevTools#3160, ChromeDevTools#3185, ChromeDevTools#3202, ChromeDevTools#3207, ChromeDevTools#3208.

Existing content in `AGENTS.md` is unchanged.

Closes ChromeDevTools#3222

🤖 I have created a release *beep* *boop*
---


##
[1.12.0](chrome-devtools-mcp-v1.11.0...chrome-devtools-mcp-v1.12.0)
(2026-10-22)


### 🎉 Features

* add --maxNavigationSaved flag to configure retained navigation history
([#3018](#3018))
([a580d13](a580d13))
* add Kimi Code plugin manifest
([#3029](#3029))
([cd00b64](cd00b64))
* Analyze heap snapshots without a browser connection
([#3156](#3156))
([78c8320](78c8320))
* **config:** add --watchConfig to reload config file changes
([#3248](#3248))
([b48561f](b48561f))
* **config:** introduce layered ServerConfig for live reload
([#3203](#3203))
([37f1fda](37f1fda))
* **config:** share ReadonlyServerConfig with McpContext and McpPage
([#3204](#3204))
([0813bf3](0813bf3))
* **config:** support reloading blockedUrlPattern and allowedUrlPattern
([#3268](#3268))
([cc850f5](cc850f5))
* **context:** release disabled feature state on config reload
([#3049](#3049))
([c0140d1](c0140d1))
* Paginate by default in heap snapshot tools
([#3201](#3201))
([fb8375b](fb8375b))
* Paginate detailed diff in compare_heapsnapshots
([#3195](#3195))
([4a9dd53](4a9dd53))
* run independent tool calls in parallel with a TaskRunner
([#3243](#3243))
([8a8d877](8a8d877))
* run page-scoped tools on different pages in parallel
([#3252](#3252))
([f8f18ac](f8f18ac))
* **server:** add McpServer.applyConfig() to reload configuration
([#3051](#3051))
([f874aeb](f874aeb))
* **slim:** support filepath in slim mode screenshot
([#3296](#3296))
([d399c4a](d399c4a))
* Sort objects for class by self size in compare_heapsnapshots
([#3205](#3205))
([f8a18c6](f8a18c6))
* **tools:** support updating ToolHandler definitions in place
([#3050](#3050))
([8064138](8064138))
* **wait_for:** support opt-in visible text matching
([#3212](#3212))
([eef92da](eef92da))


### 🛠️ Fixes

* allow paths below a filesystem-root workspace root
([#3277](#3277))
([296ccef](296ccef))
* block evaluate_script while a dialog is open
([#3196](#3196))
([545bcbb](545bcbb))
* bound take_snapshot wait and clear the geolocation override
([#3265](#3265))
([6282f54](6282f54))
* **browser:** redact WebSocket headers from connection logs
([#2901](#2901))
([3a2f91e](3a2f91e))
* capture thrown transform errors as Zod validation issues
([#3242](#3242))
([0f95c21](0f95c21))
* clear handled dialog in McpPage.getDialog()
([#3241](#3241))
([2ab93a3](2ab93a3)),
closes
[#2958](#2958)
* **cli:** disallow --slim in CLI start options
([#2987](#2987))
([#3113](#3113))
([ae3f61c](ae3f61c))
* **cli:** do not forward tool args to start
([#3114](#3114))
([fef1598](fef1598))
* **cli:** serialize object daemon arguments
([#2797](#2797))
([f73a440](f73a440))
* close the tab opened by a failed new_page
([#2928](#2928))
([c174677](c174677))
* **config:** accept native JSON objects for wsHeaders in config files
([#3262](#3262))
([371e6c2](371e6c2))
* **console:** describe Map, Set, function, DOM node, symbol and cyclic
arguments
([#3199](#3199))
([968e4e5](968e4e5))
* **console:** include the reason of unhandled promise rejections
([#3148](#3148))
([f7cdf73](f7cdf73))
* defer focus emulation until a page is explicitly targeted
([#3230](#3230))
([35abe35](35abe35))
* disable Puppeteer signal handlers for launched browsers
([#3238](#3238))
([3afec73](3afec73)),
closes
[#3154](#3154)
* discover third-party developer tools before tool lookup
([#3208](#3208))
([2777fa0](2777fa0)),
closes
[#2973](#2973)
* discover third-party developer tools in page tools
([#3207](#3207))
([cf33529](cf33529)),
closes
[#2980](#2980)
* drop InlineTextBox nodes from text snapshots
([#3202](#3202))
([f8c775a](f8c775a))
* **emulate:** keep previous viewport when setViewport fails
([#3150](#3150))
([19d883c](19d883c))
* exclude source maps from the npm package
([#3295](#3295))
([d575da4](d575da4))
* keep surrogate pairs and emoji whole when truncating titles, names and
bodies
([#3215](#3215))
([058adcf](058adcf))
* let resourceTypes match CORS preflights and prefetches
([#3217](#3217))
([e342c6e](e342c6e))
* **lighthouse:** explain unsupported URL schemes in navigation mode
([#3144](#3144))
([c6ad84a](c6ad84a))
* **lighthouse:** fail the audit when Lighthouse reports a runtime error
([#3188](#3188))
([53ea78d](53ea78d))
* **lighthouse:** restore the emulated viewport after a navigation audit
([#3189](#3189))
([c777ece](c777ece))
* **network:** list only earlier hops in a request's redirect chain
([#3198](#3198))
([4675940](4675940))
* **network:** remove unsupported websocket from list_network_requests
filter
([#2961](#2961))
([#3282](#3282))
([8b119d9](8b119d9))
* **network:** reset page network emulation before applying URL
restrictions
([#3312](#3312))
([f25f3df](f25f3df))
* **pages:** reject devtools:// URLs in navigate_page and new_page
([#2935](#2935))
([#3128](#3128))
([c94c03d](c94c03d))
* **pages:** report the actual page size after resize_page
([#2998](#2998))
([#3132](#3132))
([f003056](f003056))
* **pages:** revert reporting the page size after resize_page
([#3308](#3308))
([186ea66](186ea66)),
closes
[#3306](#3306)
* **pagination:** return all items when pageSize is omitted and pageIdx
is 0
([#2996](#2996))
([#3134](#3134))
([3ad9115](3ad9115))
* **performance:** populate structuredContent for traceInsight in
performance_analyze_insight
([#2981](#2981))
([#3115](#3115))
([c2c6cc4](c2c6cc4))
* preserve unread page fallback across snapshots and deduplicate page
disposal
([#3161](#3161))
([8604365](8604365))
* print the no-roots temp-directory warning under default flags
([#2927](#2927))
([0dd8ed9](0dd8ed9))
* reject empty, extra, and unknown parts in geolocation and viewport
transforms
([#3097](#3097))
([#3120](#3120))
([3ea31fb](3ea31fb))
* resolve error causes on the session that reported the exception
([#3220](#3220))
([b2d37e8](b2d37e8))
* resolve service worker IDs for console messages
([#2881](#2881))
([3804a9a](3804a9a))
* return message when page exposes no 3p developer tools
([#3197](#3197))
([663f3c3](663f3c3)),
closes
[#3004](#3004)
* **script:** surface non-Error thrown and rejected values in
evaluate_script
([#2951](#2951))
([#3127](#3127))
([b1e6e68](b1e6e68))
* **security:** validate filesystem paths that parse as http/ws URLs
([#3186](#3186))
([91e112d](91e112d))
* **snapshot:** omit uid for accessibility nodes without backendNodeId
([#3187](#3187))
([9054351](9054351))
* stop active screencast on McpPage.dispose()
([#3160](#3160))
([558af81](558af81))
* stop get_network_request waiting forever for an unread no-store body
([#3216](#3216))
([c556be1](c556be1))
* surface nested error causes and autoConnect hint on connection failure
([#3111](#3111))
([d7f1e78](d7f1e78))
* treat 0.0.0.0 and [::] browser endpoints as local
([#3321](#3321))
([7d5f7de](7d5f7de))
* treat IPv4-mapped IPv6 loopback as localhost
([#3255](#3255))
([6cfb34c](6cfb34c))
* truncate data: URLs in accessibility snapshots
([#3292](#3292))
([11e7d47](11e7d47))
* validate type_text submitKey before typing
([#3185](#3185))
([c8615d7](c8615d7))
* **wait_for:** find text in dynamically attached iframes
([#3210](#3210))
([5f84888](5f84888))
* warn when screenshot dimensions exceed 16384px limit
([#2952](#2952))
([#3291](#3291))
([10455b7](10455b7))


### 📄 Documentation

* add a pre-submit checklist to AGENTS.md
([#3236](#3236))
([e96ee6c](e96ee6c))
* clarify URL pattern port and hostname matching
([#3287](#3287))
([4723335](4723335))
* **config:** note that hot-reloaded URL restrictions keep open targets
attached
([#3314](#3314))
([47db2b8](47db2b8))
* correct CLI availability of extension tools
([#2852](#2852))
([a7280ee](a7280ee))
* explain how to install skills, including the CLI skill
([#3274](#3274))
([46eb546](46eb546))
* remove experimental status from CLI and promote it in README
([#3273](#3273))
([0ced16b](0ced16b))
* require a rebase only when the branch has merge conflicts
([#3239](#3239))
([d1143ac](d1143ac))
* **skills:** clarify Lighthouse score scale and contrast workflow
([#3006](#3006))
([#3218](#3218))
([bf8c6d9](bf8c6d9))


### ⚡ Performance

* **cli:** load a small third-party bundle in the chrome-devtools CLI
([#3200](#3200))
([552e1f8](552e1f8))
* load the Lighthouse bundle on first use
([#3169](#3169))
([798f03a](798f03a))


### 🏗️ Refactor

* **config:** isolate scripts and unit tests from home config discovery
([#3256](#3256))
([65e6b97](65e6b97))
* **config:** lock slim and pageIdRouting options when viaCli is set
([#3257](#3257))
([384d9aa](384d9aa))
* **config:** pass ReadonlyServerConfig to BrowserManager and add
OptionGate
([#3267](#3267))
([98302f2](98302f2))
* **config:** simplify watchConfig and start watcher inside connect
([#3259](#3259))
([878c5f6](878c5f6))
* extract errorResult() and routedPageId() in ToolHandler
([#3251](#3251))
([9a6b03a](9a6b03a))
* import types and values from a module in one statement
([#3303](#3303))
([f4eaf1f](f4eaf1f))
* **lighthouse:** move Lighthouse runner methods to McpPage and add
bundle types
([#3283](#3283))
([e1823a2](e1823a2))
* list optional properties last in inline object types
([#3302](#3302))
([dc929c0](dc929c0))
* register all tools upfront across modes
([#3163](#3163))
([58f8d1f](58f8d1f))
* **response:** pass live ReadonlyServerConfig to McpResponse
([#3258](#3258))
([6042490](6042490))
* **tools:** add explicit factory types to tool definitions
([#3284](#3284))
([4d1d7b2](4d1d7b2))
* use #private names instead of the private modifier
([#3301](#3301))
([2e13311](2e13311))

---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).