Hooks Viewer

HooksViewer is a development tool that subscribes to every Matomo event and surfaces them, in real time, while you are browsing the admin or exercising the API.

Two outputs

Inline DOM — On HTML pages and on widget AJAX requests (format=html), each fired event is rendered as a <details><summary> block at the exact place in the response stream where it was dispatched. Open the summary to see a clean, indented dump of the hook arguments.

Log file — tmp/logs/hooksviewer.log receives one line per fired event from every request, including JSON API calls, tracker hits, and CLI commands. Each line carries a timestamp, a short request id so you can correlate concurrent requests, an event index, the hook name, and a compact view of the args.

tail -f tmp/logs/hooksviewer.log

Where the hook list comes from

The plugin does not ship a hand-maintained list. On the first request after activation it scans core/ and plugins/ for every Piwik::postEvent('…') call site, resolves same-file constant references, and persists the result to tmp/cache/hooksviewer-catalog.php. The cache is invalidated whenever the source tree changes, so new events introduced by a Matomo upgrade or by a third-party plugin appear automatically.

Wildcard event names (those containing PHP variables or sprintf placeholders, e.g. Controller.$module.$action) are skipped because they cannot be subscribed to as a single static name.

Response safety

Some Matomo responses cannot tolerate any extra bytes:

• module=API (JSON / XML / CSV / TSV / RSS)
• matomo.php and piwik.php (tracker hits and image responses)
• CLI commands

For these, HooksViewer does not inject anything into the response. Use the log file (tmp/logs/hooksviewer.log) to observe their hooks.

For HTML pages and widget AJAX (format=html), output is rendered inline as <details> elements styled to stay readable on light and dark themes alike.

Useful references

• Event guide: https://developer.matomo.org/guides/events
• Core event reference: https://developer.matomo.org/api-reference/events

Reminder

This plugin exposes internal arguments (including configuration values and visitor data) and writes a log file on every request. Never install it on a production instance.

How do I install the plugin?

It is published on the official Matomo Marketplace, like any other plugin:

• Open the administration panel.
• Go to Marketplace → Plugins.
• Search for HooksViewer, install it, then activate it.

Why "never install in production"?

The plugin renders internal hook arguments into the page (database configuration, visitor IPs, request parameters, etc.) and writes a log file on every request. Both are useful while debugging and unacceptable in production.

Where do I see the hooks?

Two places, at the same time:

1. Inline in the DOM, as <details><summary> blocks placed exactly where the event was dispatched. Works on regular admin pages and on widget AJAX content (format=html).
2. In the log file at tmp/logs/hooksviewer.log. This catches every hook from every request — including JSON API calls, tracker hits, and CLI commands, where the plugin cannot safely inject markup. Tail it with tail -f tmp/logs/hooksviewer.log.

I activated the plugin but my CSS still looks unstyled.

Matomo caches the merged stylesheet bundle on disk. The plugin clears that cache on activation. If you somehow get out of sync, deactivate the plugin and reactivate it — the next request will rebuild the bundle.

How does the plugin keep up with new Matomo events?

The list of subscribed hooks is not hand-maintained. The plugin scans core/ and plugins/ for Piwik::postEvent('…') calls and caches the discovered list under tmp/cache/. The cache is rebuilt whenever the source tree changes, so new events appear automatically the next time the cache is invalidated.

Does the plugin break Matomo's API or tracker?

No. Inline output is only emitted for HTML responses (regular pages and widget AJAX with format=html). API JSON, CSV exports, XML, image responses, and tracker hits are left untouched. Use the log file to observe hooks fired during those requests.

Some hooks I expected to see are missing.

A few things to check:

• Is the event a wildcard (e.g. Controller.$module.$action)? Those are skipped because they have no fixed name to subscribe to.
• Did the event fire at all on this request? Check tmp/logs/hooksviewer.log — if it's not there either, the code path was not reached.
• Was the hook fired during a JSON API call? Inline rendering is intentionally disabled for those; check the log file.

Is the plugin active for everyone in my Matomo instance?

Yes. While it is activated, every visitor and every admin user sees the inline output and the log file grows. Deactivate it as soon as you are done debugging.

How can I contribute?

Open an issue or a pull request on https://github.com/openmost/HooksViewer.

How long will it be maintained?

As long as I keep using Matomo across projects, which is the foreseeable future. I'm the first user of this plugin — if it breaks on a Matomo upgrade I'll see it before you do.

• Hook detail

  

• Hooks list