JSON 3-Way Merge

What is a three-way merge?

A two-way merge only sees the final versions, so it can't tell whether a differing value is a deliberate change or untouched original. A three-way merge adds the common ancestor (the base), which lets it reason about intent: if only one side changed a key, that change wins automatically; if both sides made the same change, they agree; only when both sides changed the same key to different values is there a genuine conflict.

This is the same algorithm Git uses for source files — but Git merges text lines, which is noisy and error-prone for JSON. Reordered keys, re-indented blocks, or one-line documents produce spurious line conflicts. Merging structurally, key by key, eliminates that noise entirely.

How JsonDrift resolves changes

• Changed on one side only — applied automatically, no conflict
• Same change on both sides — applied once, no conflict
• Added on both sides with equal values — kept, no conflict
• Changed to different values on both sides — flagged as a conflict
• Deleted on one side, modified on the other — flagged as a conflict
• Per-conflict resolution: pick 'mine' or 'theirs' for each conflicted path
• Result preview updates instantly as you resolve

When you need a JSON three-way merge

Git merge conflicts in JSON files: package.json, tsconfig.json, translation files (en.json and friends), and CI config are the classic offenders. Copy base, mine, and theirs out of your merge tool, merge structurally here, and paste the clean result back.

Parallel config edits: two environments or two teammates edited the same deployment config from a shared original. A three-way merge combines both sets of changes without anyone's work being overwritten.

Content and data workflows: two exports of the same dataset were edited independently — merge them against the original export instead of manually reconciling.

Three-way merge vs deep merge

JsonDrift's JSON Merge tool performs a deep merge of two documents: the second document's values win wherever both define a key. That is the right tool for layering overrides — defaults plus environment config, for example.

A three-way merge is different: neither side automatically wins. The base version arbitrates, so both sides' intentional changes survive and only true collisions need a human decision. Use deep merge for layering; use three-way merge for reconciling parallel edits.

Getting the base, mine, and theirs from Git

During a conflicted merge, Git keeps all three versions in the index. Extract them with: git show :1:path/to/file.json > base.json (common ancestor), git show :2:path/to/file.json > mine.json (your branch), and git show :3:path/to/file.json > theirs.json (incoming branch). Paste each into the matching pane, resolve any conflicts, and copy the merged result back into the file.

Private, like every JsonDrift tool

All three documents are parsed and merged locally in your browser. Nothing is uploaded, so merging production configuration or customer data is safe.