Postmaster

Postmaster is a devtools panel for logging postMessages, which can be useful for debugging cross-window communication, including messages sent from iframes and MessageChannels. It includes a feature rich toolbar, making it a powerful debugging tool:

FEATURES:

LOGGING: Postmaster logs all messages with their origin, destination, time received, timestamp offset, and payload. Clear your logs at any time.

FILTERING & SEARCHING: Add filters to prevent logging of unwanted or frequent messages, reducing noise. Once messages are logged, you can search through them using the search tool. Both filtering and search support targeting messages by origin, destination, or even the data payload — includes regex support for advanced use cases.

SORT: Toggle how inbound messages are displayed, based on their time of receival.

PRETTIFY: By default, Postmaster displays all message payloads as formatted JSON when applicable. For a more compact view, you can turn this off.

PAUSE/PLAY: For debugging in scenarios with high volumes of exchanged messages, Postmaster supports a pause/play functionality to temporarily control the influx of logged messages.