Table of Contents

• About
  • Why?
  • Design
• Installation
• Usage
  • MCP server (AI assistants)
  • Supported formats
  • Pre-commit hook
  • Emacs (Apheleia)
  • VS Code
  • Neovim
  • Vim
  • Obsidian
  • Microsoft Word
  • Git smudge/clean filter
  • Vale integration
  • Project config
• Documentation
• Development
  • Key dependencies
  • Conventions
• License

About

A fast, format-aware semantic line break formatter. Reformats prose so each sentence occupies its own line, producing minimal and meaningful git diffs when collaborating on documents.

Why?

When multiple authors collaborate on a paper using Git, traditional line wrapping at a fixed column width causes problems. A single word change can trigger a diff that spans an entire paragraph. By breaking at sentence boundaries instead, each edit affects only the sentence that changed.

This convention, often called semantic line breaks, enjoys longstanding support from technical writers. Existing tools fall short: latexindent.pl only handles LaTeX, SemBr requires Python and neural networks, and most lack multi-format awareness. snapper solves this as a standalone Rust binary with no runtime dependencies, handling Org-mode, LaTeX, Markdown, and plaintext.

Design

snapper runs a three-stage pipeline:

• Parse: Classify input into prose regions and structure regions
• Split: Detect sentence boundaries in prose regions
• Emit: Output each sentence on its own line

Math environments, tables, front matter, drawers, and non-source comments pass through unchanged. Fenced and delimited source blocks are Region::Code: fence/open/close lines stay structure, non-comment code stays verbatim, and comment lines reflow at sentence boundaries when the language has a [code.<lang>] entry in .snapperrc.toml (snapper init seeds common languages). Pass --format-code to also pipe each block body through an optional per-language formatter argv (missing binary, non-zero exit, and timeouts degrade to the reflowed body). Sentence detection relies on Unicode UAX #29 segmentation with abbreviation-aware post-processing that avoids false breaks at titles (Dr., Prof.), references (Fig., Eq.), and Latin terms (e.g., i.e., et al.). Org emphasis (*bold*, /italic/, _underline_, +strike+) is kept atomic so splits cannot open a pseudo-headline mid-span.

Installation

Pre-built binary (fastest):

cargo binstall snapper-fmt

Shell one-liner (Linux/macOS):

curl -LsSf https://github.com/TurtleTech-ehf/snapper/releases/latest/download/snapper-fmt-installer.sh | sh

Homebrew:

brew install TurtleTech-ehf/tap/snapper-fmt

pip:

pip install snapper-fmt

Compile from source:

cargo install snapper-fmt

Nix:

nix build github:TurtleTech-ehf/snapper

The crate is snapper-fmt on all registries. Each install ships two CLI names for the same program: snapper and snapper-fmt.

Name collision: openSUSE snapper is a different project (Btrfs/LVM snapshots) that also installs a snapper binary. On systems where that tool already owns /usr/bin/snapper, call this formatter as snapper-fmt, or put the TurtleTech install path ahead of the system path.

Pre-built installers (cargo-dist) ship the plain binaries: native Org/LaTeX/Markdown/RST parsers, no GHC, no embedded pandoc. Multi-format pandoc is opt-in at runtime or via an optional build feature (below).

Usage

Format a file (output to stdout):

snapper paper.org

Format in place:

snapper --in-place paper.org

Pipe through stdin (for editor integration):

cat draft.org | snapper --format org

Check formatting without modifying (for CI):

snapper --check paper.org paper.tex notes.md

Limit line width (wrap long sentences at word boundaries):

snapper --max-width 80 paper.org

Preview changes as a unified diff before committing:

snapper --diff paper.org

Compare two versions at the sentence level (whitespace reflow produces zero diff):

snapper sdiff paper_v1.org paper_v2.org

Watch files and auto-reformat on save:

snapper watch '*.org' 'sections/*.tex'

Initialize a project (generates config, pre-commit, gitattributes):

snapper init

Pandoc backend (optional multi-format)

Parse with pandoc, then reflow only prose from the AST (headers, code, tables, math stay structure):

# Uses system `pandoc` on PATH (JSON CLI), or in-process FFI if available
snapper --use-pandoc paper.typ
snapper --use-pandoc --pandoc-backend cli guide.adoc
snapper --use-pandoc --pandoc-backend ffi paper.md   # needs libsnapper_pandoc or colink build

• CLI backend (default when FFI is missing): install the normal pandoc binary.
• FFI backend: build native/snapper-pandoc and set SNAPPER_PANDOC_LIB, or build with feature pandoc-colink after ./native/snapper-pandoc/build-static.sh so one binary absorbs the static archive (no env discovery; larger binary; not the default release artifact).
• UPX (optional third-party packer) can shrink on-disk size of a finished static-colink binary via ./native/snapper-pandoc/pack-upx.sh; it is not a tree-shaker and is not part of default CI or cargo-dist. See native/snapper-pandoc/README.md.

MCP server (AI assistants)

Expose snapper's tools to Claude Desktop, Claude Code, and other MCP clients:

npx @turtletech/snapper-mcp

Or directly:

snapper mcp

Tools: format_text, detect_format, check_formatting, split_sentences. Configuration guide (org source in-tree): docs/orgmode/howto/mcp-integration.org; HTML docs: https://snapper.turtletech.us/docs/howto/mcp-integration/ .

Supported formats

Pre-commit hook

- repo: https://github.com/TurtleTech-ehf/snapper
  rev: v0.8.1
  hooks:
    - id: snapper

Runs snapper --in-place on *.org, *.tex / *.latex, *.md / *.markdown, *.rst, and *.txt (matched by extension; pre-commit's identify database has no org type). Requires a Rust toolchain so pre-commit can build the hook from this repo.

Emacs (Apheleia)

(with-eval-after-load 'apheleia
  (push '(snapper . ("snapper" "--format" "org")) apheleia-formatters)
  (push '(org-mode . snapper) apheleia-mode-alist))

VS Code

Install TurtleTech.snapper from the VS Code Marketplace. The extension uses the built-in LSP server for format-on-save, range formatting, diagnostics, and code actions.

Neovim

With lazy.nvim (rocks support):

{
  "TurtleTech-ehf/snapper",
  ft = { "org", "tex", "markdown", "rst" },
  config = function()
    vim.opt.runtimepath:append(
      vim.fn.stdpath("data") .. "/lazy/snapper/editors/nvim"
    )
    require("snapper").setup()
  end,
}

Or with rocks.nvim:

:Rocks install snapper.nvim

Vim

Plug 'TurtleTech-ehf/snapper', { 'rtp': 'editors/vim' }

This provides formatprg support for automatic formatting with the gq operator.

Obsidian

Install the snapper plugin from Community Plugins (search "Snapper"). Uses WebAssembly -- no binary installation required.

Microsoft Word

Install the snapper add-in from AppSource (Insert > Get Add-ins > search "Snapper"). Uses WebAssembly -- no binary installation required.

Git smudge/clean filter

Auto-format on commit, transparent to collaborators:

git config filter.snapper.clean "snapper --format org"
git config filter.snapper.smudge cat

Then add to .gitattributes:

*.org filter=snapper

Vale integration

snapper ships a vale style package for editor hints. Add to your .vale.ini:

StylesPath = /path/to/snapper/vale
[*.org]
BasedOnStyles = snapper

For precise CI checks, use snapper --check directly.

Project config

Drop a .snapperrc.toml in your project root:

extra_abbreviations = ["GROMACS", "LAMMPS", "DFT"]
ignore = ["*.bib", "*.cls"]
format = "org"
max_width = 0

snapper walks up from the current directory to find it.

Documentation

Build the docs site with:

pixi run docbld

Development

Key dependencies

• Clap 4 (derive): CLI argument parsing
• unicode-segmentation: UAX #29 sentence boundaries
• regex: Abbreviation and format pattern matching
• textwrap: Optional line width limiting
• thiserror: Typed error handling

Conventions

We use cocogitto via cog to handle commit conventions.

Readme

Construct the readme via:

./scripts/org_to_md.sh readme_src.org README.md

License

MIT.