A semantic diff engine using Tree-sitter.
Diffmantic is a structural diff tool written in Go. Instead of showing line-by-line differences, it parses your code into ASTs and matches nodes. This lets it track moved functions, in-place updates, and structural shifts, not just added or deleted lines.
Note: The editor integrations (VS Code, Neovim) and TUI are under active development.
- Go
- JavaScript / TypeScript
- Python
- Move Detection: Knows when you move a block of code, instead of showing it as deleted and re-added.
- Update Detection: Shows when you change part of a node (like a string label or variable name).
- Insert / Delete: Pinpoints exactly where structure was added or removed.
- Stable Paths: The JSON output points to nodes using child-index paths (e.g.
[0, 2, 1]) instead of line numbers, so editor plugins don't lose track of highlights as you edit.
Install the CLI using the install script:
curl -fsSL https://raw.githubusercontent.com/HarshK97/diffmantic/main/install.sh | shBy default, this installs the diffm binary to ~/.local/bin. Make sure that folder is in your $PATH.
Diff two files using:
diffm diff before.go after.goBy default, this outputs structured JSON (schema version v1) designed for editor plugins and automation.
If you want a human-readable list of edit actions, run:
diffm diff before.go after.go -f actionsDiffmantic matches ASTs in four main steps:
- Top-Down Matching: We look for identical subtrees of the same height first. When we find an exact match, we map those nodes and their children recursively.
- Bottom-Up Matching: For unmatched nodes, we look for counterparts of the same type that share already-matched children. We match them if their similarity score is high enough.
- Recovery: Inside matched containers, we run Longest Common Subsequence (LCS) on unmatched children. We do this twice: once using exact labels, and once using structure only.
- Action Generation & Post-Processing: We generate a raw edit script (insert, delete, update, move) and refine it. We collapse child edits into clean subtree edits (like a whole folder/block insert), normalize comment updates, and group moved elements together.
MIT License - see LICENSE.
Our engine is based on the GumTree matching algorithm. You can check out the details here: