Deep-merge YAML documents with Helm-style overrides

About this tool

This tool deep-merges multiple YAML documents into one YAML result. Paste a ----separated stream the same way you would layer several Helm values files: the first document is the base, each later document overrides it, and the merged YAML is produced locally in your browser.

The default mode matches the common Helm mental model:

• mappings merge recursively;
• when two scalar values conflict, the later document wins;
• arrays are replaced by the later document;
• a key set to null in a later document deletes that key.

Those defaults are useful for Kubernetes and application config, but the controls let you choose stricter or more expansive behavior. Use Conflict precedence to keep the first value or reject conflicts, Array merge to append or merge lists, Array item key to line up object-list entries such as containers or environment variables by name, and Sort keys A-Z when you want a stable alphabetized output for diffs.

Worked example

Input:

image:
  repository: app
  tag: "1.0"
replicas: 1
service:
  ports:
    - 80
---
image:
  tag: "2.0"
service:
  ports:
    - 443

Merged result with defaults:

image:
  repository: app
  tag: "2.0"
replicas: 1
service:
  ports:
    - 443

image.repository stays from the base document, image.tag is overridden by the second document, and service.ports is replaced because Helm-style array merging uses replacement by default.

Array merge modes

• Replace arrays keeps the winning document's list. This is the default and matches Helm values layering.
• Append arrays concatenates the base list and override list.
• Append unique items concatenates, then removes duplicate YAML values while preserving first-seen order.
• Merge object lists by key lines up mapping items whose array_key field matches, then deep-merges those pairs. The default key is name, which fits Kubernetes-style env, containers, and similar lists.

Limits and edge cases

• Input is capped at 1 MiB and 20 YAML documents per merge.
• The output is canonical YAML, not a byte-for-byte patch. Comments, blank-line layout, tags, and anchors are not preserved by the YAML value model.
• Empty documents are ignored, just like empty values files.
• null deletes keys only when Null deletes keys is enabled. Turn it off when you need key: null to remain in the final YAML.
• Error on conflict reports the key path that disagreed. Identical values and newly added keys are still allowed.
• Shallow top-level merge replaces entire nested subtrees below a top-level key instead of recursively merging them.

FAQ