#264 · Developer Tool

YAML Duplicate Key Detector

Find repeated YAML mapping keys that may be silently overwritten by a parser. The detector tracks indentation-based mapping paths and reports the first and repeated line for each duplicate. Identical key names in different parent mappings are kept separate, while each YAML document receives its own scope. Comments, blank lines, sequence markers, and quoted key names are handled conservatively to keep the report useful for configuration reviews.

Developer Input

YAML source
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How to use this developer tool

  1. Paste or upload the yaml source you want to inspect.
  2. Run Find Duplicate Keys, or press Ctrl/Cmd + Enter.
  3. Read the summary, diagnostics, and reported counts before using the output.
  4. Copy the result or download it in the shown format.

What this developer tool does

The detector builds a lightweight mapping path from indentation and compares keys within the same parent. Each hit includes its full path and both line numbers.

A duplicate is defined as the same normalized key appearing twice at one mapping level in a document. The check does not treat the same key under different parents as a conflict.

Many YAML parsers accept duplicate keys and keep only the last value. Fix every reported entry unless your parser has a documented alternative policy.

Example

The Sample button loads a representative yaml source. Running it produces the same kind of duplicate key report shown in the result panel, including counts that are calculated from the supplied text rather than fixed examples.

database:
  host: localhost
  port: 5432
  host: db.internal
logging:
  level: info
  level: debug

Use cases

  • Review configuration changes before committing them.
  • Diagnose format-specific problems in CI or deployment inputs.
  • Create a copy-ready result for documentation or another developer tool.
  • Check generated files without exposing project data to a remote service.

Tips for reliable output

  • Start with the smallest input that reproduces a problem.
  • Keep a copy of the original before replacing configuration files.
  • Read warnings and limitations, even when the main result succeeds.
  • Validate the output again with the parser used by your application.
  • Use UTF-8 when saving downloaded text.

Processing details

The scan is linear in the number of lines and never evaluates tags, aliases, or application-specific types. Source text stays in the browser.

Complex flow mappings written entirely inside braces and explicit mapping-key syntax may need a full YAML parser. This focused check does not certify general YAML validity.

Frequently asked questions

Does YAML Duplicate Key Detector upload my input?

No. Processing runs in your browser, and the page does not send the supplied text to an API.

What input should I use with YAML Duplicate Key Detector?

Paste plain YAML text; line endings and Unicode content are accepted.

Will the output cover every edge of the format?

Complex flow mappings written entirely inside braces and explicit mapping-key syntax may need a full YAML parser. This focused check does not certify general YAML validity.

What happens when the input is invalid?

The run stops and the error area identifies the first problem the tool can locate. No partial result is presented as complete.

Can I save the result?

Yes. Copy the output, download the primary result, or use the structured JSON or CSV download when those buttons appear.

Tool details

CategoryData & Format Tools
InputYAML source
Primary outputDuplicate key report
Runs locallyYes
Data & Format ToolsBrowse JSON, YAML, TOML, XML, and structured-data utilities.Open category →