Non-serializable attributes break automation traces: `TypeError: keys must be str, int, float, bool or None`

[davidrapan]

The problem

The issue occurs during automation trace view if some attributes of the entities used within automation triggers for example contain non-serializable types such as datetime.datetime:

Logger: homeassistant.components.websocket_api.http.connection
Source: components/trace/websocket_api.py:79
integration: Home Assistant WebSocket API ([documentation](https://www.home-assistant.io/integrations/websocket_api), [issues](https://github.com/home-assistant/core/issues?q=is%3Aissue+is%3Aopen+label%3A%22integration%3A+websocket_api%22))
First occurred: 10:21:52 PM (12 occurrences)
Last logged: 10:41:36 PM

[281472370093216] Error handling message: Unknown error (unknown_error) David from 192.168.144.155 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36 Edg/138.0.0.0)
[281472316443200] Error handling message: Unknown error (unknown_error) David from 192.168.144.155 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36 Edg/138.0.0.0)
[281472237024288] Error handling message: Unknown error (unknown_error) David from 192.168.144.155 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36 Edg/138.0.0.0)
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/websocket_api/decorators.py", line 28, in _handle_async_response
    await func(hass, connection, msg)
  File "/usr/src/homeassistant/homeassistant/components/trace/websocket_api.py", line 79, in websocket_trace_get
    json.dumps(message, cls=ExtendedJSONEncoder, allow_nan=False)
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
          ~~~~~~^^^^^
  File "/usr/local/lib/python3.13/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/local/lib/python3.13/json/encoder.py", line 261, in iterencode
    return _iterencode(o, 0)
TypeError: keys must be str, int, float, bool or None, not datetime.datetime

There is an inconsistency of handling (reading of entity state and attributes) because some flows are casting these types to str (for example, displaying entity details -> Attributes which is using isoformat() directly, since the default separator 'T' is used while __str__ cast would call isoformat(sep=' ')) and some do not (automation trace view), and therefore fail.

• Migrated issue from Non-serializable attributes break automation traces: Uncaught (in promise) in ha-automation-trace.ts and TypeError: "invalid key" in websocket_api frontend#24931

What version of Home Assistant Core has the issue?

core-2025.6.1

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant OS

Integration causing the issue

Troubleshooting automations

Link to integration documentation on our website

https://www.home-assistant.io/integrations/trace

[home-assistant]

Hey there @home-assistant/core, mind taking a look at this issue as it has been labeled with an integration (websocket_api) you are listed as a code owner for? Thanks!

Code owner commands

Code owners of websocket_api can trigger bot actions by commenting:

• @home-assistant close Closes the issue.
• @home-assistant rename Awesome new title Renames the issue.
• @home-assistant reopen Reopen the issue.
• @home-assistant unassign websocket_api Removes the current integration label and assignees on the issue, add the integration domain after the command.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component) to the issue.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component) on the issue.

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websocket_api documentation
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[davidrapan]

Sorry, I originally set up the wrong integration, could someone relabel the issue?

[frenck]

Which integration is causing this issue?

As in, which integration provided non-serliazable keys as attributes?

[davidrapan]

A custom one, but I don't think it's a matter of which integration provided the keys, but it highlights the inconsistency in how other parts of HA handle this situation well besides the tracing integration.

[frenck]

but I don't think it's a matter of which integration provided the keys,

I disagree, as this is an issue with that integration.

[davidrapan]

I mean I'm not actually opposing, the integration should provide serializable types, but at the same time I would expect HA to behave consistently, thus entity detail view -> Attributes for example should give the same result (error, or automation tracing be able to crunch it anyway, both are fine by me) + maybe display it somewhat better than a blank page?

Edit: Are these constraints documented anywhere? Because the developer portal is not saying much, just that the type of extra_state_attributes is dict and then the source code uses then annotation dict[str, Any] and that's it (as the only other point of the narrower specification) so the developer should find out through trial and error?

Edit2: Note that using a Decimal in the extra_state_attributes breaks even more (but the same case of non-serializability), but is at the same time considered okay as native_value..