YAML Merger

THE PRACTICAL GUIDE · NORMANDIN SYSTEMS

Get more from YAML Merger

YAML Merger helps you merge structured documents in YAML. A deep merge combines mapping content using a defined rule for overlaps instead of simply concatenating source text. This is useful when the information is already available but its structure, presentation, or consistency makes it difficult to inspect. Work with a representative sample first so that you can recognize the expected result before applying the same operation to a larger document. Anchors, aliases, comments, and source formatting are different from the parsed data being merged. Do not assume they will be preserved. Keep the original input available while reviewing the output. The important check is whether the result still has the intended values and relationships, rather than whether it merely looks neater. Test a conflicting scalar and a sequence to understand the resulting override behavior.

Guide updated October 13, 2026

How to use this tool

1. Place the YAML input in the relevant editor. If the tool compares or combines documents, keep each document in its own input.
2. Select the available settings for the operation you need. Test a conflicting scalar and a sequence to understand the resulting override behavior.
3. Review any syntax errors before interpreting the result. A valid document with the wrong structure needs a different fix from malformed input.
4. Inspect the changed portion and at least one unchanged portion. Keep a copy of the original YAML until the result has been checked in its destination.

SEE IT IN PRACTICE

A worked example

First: a: 1; second: b: 2

a: 1
b: 2

Different keys can coexist in the merged mapping. Shared keys and sequences need separate tests.

Merged data versus source documents

A parsed-data merge generally does not preserve the original comments or anchor layout. Treat the result as a new representation of the combined values. Check sequence handling and conflict direction with a sample containing overlapping keys. If comments record operational reasons for a setting, retain that documentation separately rather than assuming the merge carries it forward.

Test overlapping sequences

Two YAML mappings with different keys combine straightforwardly, but overlapping arrays require a policy. Replacing a sequence, appending its items, and merging items by index produce different configurations. Use a two-item example with one conflict to see the actual result. Check whether null is treated as a value or given special significance, and keep the source files until the combined configuration has been accepted by the consuming application.

When this tool is useful

• Combine configuration fragments while keeping the underlying structure visible.
• Reproduce a YAML override issue with a compact, reproducible sample.
• Assemble a test configuration before copying data into another application.

Tips for a better result

• Anchors, aliases, comments, and source formatting are different from the parsed data being merged. Do not assume they will be preserved.
• Test a conflicting scalar and a sequence to understand the resulting override behavior.
• Use a small YAML example to isolate an unexpected result. Add nested objects, arrays, quoted text, and empty values only as needed to reproduce the behavior.

Frequently asked questions