What causes "YAMLException: duplicated mapping key"?

Copy-pasting a block that already exists in the file Merging two YAML files that have overlapping keys A key defined at the top level and again inside an anchor

YAML Error2 Fixes Available

YAML duplicate key warning

YAMLException: duplicated mapping key

What does this error mean?

YAML does not allow the same key to appear twice in the same mapping (object). If it does, the behavior is undefined — some parsers use the last value, others throw an error. This is a common mistake when merging YAML files.

Common Causes

Copy-pasting a block that already exists in the file
Merging two YAML files that have overlapping keys
A key defined at the top level and again inside an anchor

How to Fix It (2 Solutions)

Validate with our YAML Validator

Our validator will highlight duplicate keys instantly.

Search for the duplicate key

Use your editor's search to find all occurrences of the key name.

Code

# Use grep to find duplicate keys in a YAML file
grep -n "^  myKey:" your-file.yaml

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Related Errors

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YAMLException: bad indentation of a mapping entry

View fix

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