YAML Merge Tool

1. Use browse files, or fill Paste a YAML source, optionally add Source name, and click Add source.
2. Check the source order. It affects First source wins, Last source wins, and Concatenate (append in source order).
3. Choose a Pairing mode for single documents or matching multi-document streams.
4. Set Merge mode, Precedence for scalar & type conflicts, Null policy, and Global sequence handling.
5. Set the policies for Anchors (&) & aliases (*), Merge keys (<<), Comments, and Document boundaries (multi-document sources).
6. Review the preview and logs, then click Export merged YAML or Export merge report (JSON).

Merge YAML documents with the right pairing mode

Pair by document position across streams (source counts must match) combines document 1 from every source, then document 2. Counts must match, with one output document for each position.

Treat each source as exactly one document requires one document per source. A multi-document source blocks this mode.

Choose YAML merge rules for nested keys and sequences

Deep (recursive merge at every level) combines child keys inside nested mappings. Shallow (top-level keys only) replaces a nested mapping as one value. Last source wins and First source wins choose conflicting scalars, types, and replacement sequences.

Sequence choices are Replace (precedence picks one sequence), Concatenate (append in source order), Union (dedupe by full value, order preserved), and Merge by key (sequences of mappings). Add a dot-notated path such as items with Add path override for a local rule. An empty key field falls back to replacement; items without it remain raw.

Two sources with separate fields produce this output:

base.yaml:
port: 80

override.yaml:
host: app

merged:
port: 80
host: app

What YAML Merge Tool does with nulls, comments, and aliases

Null is a value (can win/lose conflicts normally) includes explicit null values in conflict resolution. Null means absent (ignored unless every source is null) ignores null when another value exists.

Expand to value before merge, log every occurrence resolves anchors and aliases before merging. The blocking choice stops the merge when one appears. The merge-key policy treats << as pre-resolved and logs it, or blocks that source. With Proceed, log that comments are discarded (never preserved on output), comments are dropped during parsing and serialization.

Review conflicts and blocked YAML merges

The result workspace shows Merged YAML preview, Every conflict & resolution, and Unsupported / logged constructs. Conflict entries show paths, candidate values, rules, sources, and output values. Logged constructs include source and line when available.

Malformed YAML, unequal document counts in position mode, a multi-document source in single mode, or a blocking policy prevents the merge. The parser can reject YAML syntax it does not handle. The tool does not check an external schema.

Layered YAML examples

Load base.yaml first and override.yaml second when the second source should take precedence. Set Last source wins, then inspect conflicts before exporting.

For lists of mapping objects, choose Merge by key (sequences of mappings) and enter a field in Global sequence merge key field. Entries with the same field value are merged; entries without it remain raw.

Merge output versus a YAML diff

This page produces merged YAML, a conflict log, and a construct log. It does not compare versions or validate an external schema. The Config File Merge Tools category lists other merge pages.

Frequently asked questions