Explore Available Custom Dimensions in Your Logs

Before using a custom dimension, it helps to know what keys actually exist in your data.

View Raw Custom Dimensions

Start by inspecting a few records:

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| take 5
| project customDimensions

This shows the full dynamic object so you can see available keys and example values.

List All Keys Found in the Data

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| summarize by tostring(bag_keys(customDimensions))

This returns a list of keys across your dataset.

Correct Way to Access a Key

tostring(customDimensions["UserId"])

Avoid this pattern — it does not work:

customDimensions.UserId

Tips

• Key names are case-sensitive.
• Some records may not contain the same keys.
• Always test with a small sample before building complex queries.

These discovery steps prevent mistakes and make your queries more reliable from the start.