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feat(config): add ConfigWatcher to watch config file changes by Lightning00Blade · Pull Request #3139 · ChromeDevTools/chrome-devtools-mcp · GitHub
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feat(config): add ConfigWatcher to watch config file changes - #3139

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Oct 15, 2026
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cd4a-config/5a-config-watcher

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@Lightning00Blade Lightning00Blade commented Oct 14, 2026 •

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Adds a standalone ConfigWatcher utility in src/config/ConfigWatcher.ts that watches a configuration file and invokes an async onChange callback when its contents change:

  • Symlink & atomic-save support: Resolves symlinks on start and watches the parent directory of the real file so atomic saves (writing a temp file and renaming over the target) continue to be detected.
  • Debouncing: Debounces rapid filesystem events using DevTools.Common.Debouncer.
  • Content-change filtering: Compares file contents before invoking onChange to ignore no-op writes and stale filesystem events.
  • Lifecycle management: Implements Disposable to cancel pending debounced calls and close the underlying fs.FSWatcher.
    Integration with --watchConfig and McpServer will follow in a separate PR.

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Please check the following:

  1. In src/config/ConfigWatcher.ts, skip the debounced callback when readContent(realPath) returns undefined instead of storing undefined in #content and invoking onChange. Otherwise a transient unreadable/missing file (mid-rename, or a deleted config) triggers onChange while the file cannot be read, and then a second onChange once it reappears, so the consumer would try to reload a missing config.

  2. In src/config/ConfigWatcher.ts, serialize onChange invocations (e.g. chain onto a #pending promise) rather than fire-and-forget from the debounced callback. A second change arriving while a previous onChange() is still in flight currently runs two concurrent reloads whose effects can interleave or apply out of order.

  3. In src/config/ConfigWatcher.ts, move getErrorMessage to a shared util (e.g. src/utils/errorHandling.ts) instead of duplicating the identical helper from src/config/ConfigParser.ts. Two private copies of the same function will drift.

Nits (optional)

  • tests/config/ConfigWatcher.test.ts: positive-path tests could poll for onChange.called with a bounded timeout instead of a fixed wait(SETTLE_MS), which both shortens the suite and reduces flakiness on slow CI.
  • tests/config/ConfigWatcher.test.ts: detects atomic replacements uses sinon.assert.called while the sibling tests assert calledOnceWithExactly; if a single rename can produce two calls, that is a symptom of change (1) above and should be tightened once fixed.
  • src/config/ConfigWatcher.ts: document that start() throws when configPath does not exist (fs.realpathSync) so the --watchConfig integration handles it explicitly.

@Lightning00Blade
Lightning00Blade force-pushed the cd4a-config/5a-config-watcher branch from 143ed22 to 9a7a7dd Compare October 14, 2026 16:44
Adds a standalone ConfigWatcher utility that watches a configuration file and invokes an async onChange callback when its contents change:

- Resolves symlinks on start and watches the parent directory of the real file so atomic saves (temp file + rename) continue to be detected.
- Filters directory events to the target filename when provided by the platform.
- Debounces rapid filesystem events using DevTools.Common.Debouncer.
- Compares file contents before invoking onChange to ignore no-op writes or stale platform events.
- Implements Disposable for clean watcher and timer teardown.
@OrKoN
OrKoN force-pushed the cd4a-config/5a-config-watcher branch from 9a7a7dd to 7777c8c Compare October 15, 2026 07:05
@OrKoN
OrKoN enabled auto-merge October 15, 2026 07:05
@OrKoN
OrKoN added this pull request to the merge queue Oct 15, 2026
Merged via the queue into main with commit 9171f77 Oct 15, 2026
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@OrKoN
OrKoN deleted the cd4a-config/5a-config-watcher branch October 15, 2026 07:30
OrKoN added a commit that referenced this pull request Oct 15, 2026
🤖 I have created a release *beep* *boop*
---


##
[1.11.0](chrome-devtools-mcp-v1.10.1...chrome-devtools-mcp-v1.11.0)
(2026-10-15)


### 🎉 Features

* add --file-navigations flag to reject file: URL navigations
([#2853](#2853))
([54cae57](54cae57))
* Add analyze_heapsnapshot_contexts MCP tool
([#2791](#2791))
([190aeee](190aeee))
* add ignoreCache option to performance_start_trace
([#2931](#2931))
([3467d40](3467d40))
* add maxNameLength truncation option to compare_heapsnapshots
([#3098](#3098))
([1e1c53e](1e1c53e))
* Add pagination to compare_heapsnapshots
([#3140](#3140))
([daebfd1](daebfd1))
* **config:** add ConfigWatcher to watch config file changes
([#3139](#3139))
([9171f77](9171f77))
* discover the config file in predefined locations
([#2876](#2876))
([02c0112](02c0112))
* implement ffmpeg-free screencast tools enabled by default
([#3123](#3123))
([8953ea5](8953ea5))
* reduce StaticText noise in text snapshots
([#2895](#2895))
([4441325](4441325))
* report pages opened by input actions
([#2679](#2679))
([28fb230](28fb230))
* resolve config defaults after merging CLI and config file
([#2849](#2849))
([bdeb70d](bdeb70d))
* return failing audits and DOM nodes inline from lighthouse_audit
([#2930](#2930))
([241fba5](241fba5))
* skip more redundant data in text snapshots
([#2896](#2896))
([b2f522c](b2f522c))
* support debugging WebMCP tools in third-party developer tools
([#2900](#2900))
([0db519f](0db519f))
* support emulating additional CSS media features
([#2929](#2929))
([69524f0](69524f0))
* support evaluating scripts from local files
([#2606](#2606))
([9cf47a4](9cf47a4))
* Support truncation in get_heapsnapshot_details
([#3137](#3137))
([f827e06](f827e06))
* Truncate long names by default to 100 characters
([#2893](#2893))
([5ddb0a3](5ddb0a3))


### 🛠️ Fixes

* account for scroll offsets in downscaled screenshots
([#2685](#2685))
([830c693](830c693))
* allow --categoryExtensions when connecting to an existing browser
([#3041](#3041))
([d250bc5](d250bc5))
* allow stopping the CLI if command fails
([#3088](#3088))
([77e238e](77e238e)),
closes
[#2982](#2982)
* avoid runtime title fetches
([#2883](#2883))
([04195d1](04195d1))
* better config support for chrome-devtools CLI
([#2819](#2819))
([9624e64](9624e64))
* clamp async stack trace separator repeat count
([#3035](#3035))
([93e06ab](93e06ab)),
closes
[#3031](#3031)
* **cli:** pass positional values starting with `-` through to tools
([#3084](#3084))
([9de05ae](9de05ae)),
closes
[#2984](#2984)
* **collectors:** ignore transient target errors when subscribing to
service workers
([#2888](#2888))
([551dd6c](551dd6c))
* **daemon:** bound browser shutdown and avoid watchFile timeout on stop
([#2887](#2887))
([f3db5e7](f3db5e7))
* **daemon:** keep fallback socket in private runtime dir
([#2766](#2766))
([871a37e](871a37e))
* **daemon:** verify process identity before treating PID file as active
([#3109](#3109))
([b608bed](b608bed))
* do not close a healthy browser when a tool call outlasts 60s
([#3149](#3149))
([39c7db1](39c7db1))
* ensure aggregate IDs in heap snapshots are deterministic
([#2923](#2923))
([e918c47](e918c47))
* escape client-supplied values in McpContext logs and errors
([#2832](#2832))
([efb0d02](efb0d02)),
closes
[#2831](#2831)
* fail fast on tool calls stuck after a dead browser connection
([#2699](#2699))
([2a7ef50](2a7ef50))
* harden third-party tool result serialization
([#2892](#2892))
([4418a7b](4418a7b))
* honor explicit --allowUnrestrictedPaths=false in CLI mode
([#3040](#3040))
([61fc362](61fc362))
* include errors in slim responses
([#3085](#3085))
([ee38097](ee38097))
* **input:** reject multiple file paths on single-file input in
upload_file
([#2995](#2995))
([#3135](#3135))
([e650843](e650843))
* list fresh page titles
([#3103](#3103))
([e717082](e717082))
* **memory:** reject contradictory pagination options in
take_heapsnapshot
([#3002](#3002))
([#3131](#3131))
([508126c](508126c))
* **network:** enforce URL policy across redirects
([#2767](#2767))
([274cd4c](274cd4c))
* pass categoryExtensions to the target filter when connecting
([#3047](#3047))
([4e90238](4e90238))
* **performance:** report an error when performance_stop_trace is called
with no active trace
([#3001](#3001))
([#3126](#3126))
([e170384](e170384))
* preserve HeapSnapshotManager across browser reconnects
([#3025](#3025))
([64388c6](64388c6))
* propagate failed responseFilePath write error instead of reporting
body unavailable
([#2957](#2957))
([#3119](#3119))
([3cee3bd](3cee3bd))
* **pwa:** wait for initial navigation on launch and retry transient
install error
([#2889](#2889))
([63010cb](63010cb))
* record screencast at the page's device pixel size
([#3155](#3155))
([62e2aa4](62e2aa4))
* reject --blockedUrlPattern/--allowedUrlPattern hostname regexp groups
([#2796](#2796))
([ae0aaef](ae0aaef))
* reject JSON arrays as 3p and WebMCP tool params
([#2785](#2785))
([c14e616](c14e616))
* reject named groups in URL patterns
([#2857](#2857))
([5b2c6f9](5b2c6f9))
* reject non-positive --viewport dimensions
([#2781](#2781))
([0ef528a](0ef528a))
* reject non-positive resize_page dimensions
([#2784](#2784))
([6ab6d35](6ab6d35))
* reject unrestricted paths with an explicit workspace
([#2858](#2858))
([45c1c6c](45c1c6c))
* report unknown page id before last-page guard in close_page
([#3042](#3042))
([bdc7e24](bdc7e24))
* round lighthouse category scores and show unscored categories as n/a
([#2924](#2924))
([7007680](7007680)),
closes
[#2915](#2915)
[#2916](#2916)
* set empty filePath to undefined instead of empty string
([#2836](#2836))
([adfc1ff](adfc1ff)),
closes
[#2825](#2825)
* surface WebMCP tool exceptions in execute_webmcp_tool
([#3107](#3107))
([d80d22e](d80d22e)),
closes
[#2975](#2975)
* url pattern partial ipv4
([#2859](#2859))
([c87d190](c87d190))


### 📄 Documentation

* clarify Antigravity MCP setup for VS Code extension
([#2855](#2855))
([12e13ca](12e13ca))
* clarify scope of --no-javascript-evaluation
([#3100](#3100))
([0c67cd5](0c67cd5))
* correct link to configuration
([#3086](#3086))
([bbb1e36](bbb1e36))
* document trusted host environment in SECURITY.md
([#3125](#3125))
([1352207](1352207))
* fix inaccurate examples in skills and CLI docs
([#2922](#2922))
([ec372b0](ec372b0)),
closes
[#2906](#2906)
[#2907](#2907)
[#2908](#2908)
[#2910](#2910)
[#2912](#2912)
[#2913](#2913)
[#2918](#2918)
[#2919](#2919)
[#2920](#2920)
[#2921](#2921)
* fix some reported issues
([#3099](#3099))
([d5d2f08](d5d2f08))
* include serviceWorkerId parameter for evaluate_script
([#3015](#3015))
([#3129](#3129))
([0623434](0623434))
* mention heapsnapshot being cached between runs
([#3045](#3045))
([f08dbe1](f08dbe1)),
closes
[#2976](#2976)
* **skills:** remove invalid outputDir flag from lighthouse_audit calls
([#3013](#3013))
([#3130](#3130))
([7754226](7754226))
* update documentation and SKILL for get_css_styles tool
([#2824](#2824))
([3c12a91](3c12a91))


### ⚡ Performance

* **cli:** re-use MCPServer.from helpers for daemon
([#2804](#2804))
([89eb3d5](89eb3d5))
* Load heap snapshots in parallel in compare_heapsnapshots
([#3023](#3023))
([20c1391](20c1391))


### 🏗️ Refactor

* centralize config defaults and conflict checks
([#2753](#2753))
([a739ba8](a739ba8))
* create all tools and register per slim mode
([#2874](#2874))
([99847a7](99847a7))
* enable categories by default
([#2811](#2811))
([e33ee48](e33ee48))
* extract CLI examples and conflict list in mcp-options
([#2848](#2848))
([45000d9](45000d9))
* extract config parsing logic in a class
([#2861](#2861))
([e4168d0](e4168d0))
* extract worker logic into McpWorker
([#2800](#2800))
([77165c6](77165c6))
* group Puppeteer and tool options
([#2875](#2875))
([699c4d5](699c4d5))
* lazily initialize McpPage from Target and enumerate targets in
McpContext
([#2812](#2812))
([545cbe3](545cbe3))
* use default Error for toolSchema
([#2822](#2822))
([8b2768d](8b2768d))

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

Co-authored-by: Alex Rudenko <OrKoN@users.noreply.github.com>
zjdCander pushed a commit to zjdCander/chrome-devtools-mcp that referenced this pull request Oct 19, 2026
## 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
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