Know Thyself. Automatically Check Spelling and Grammar on Git Commits

Published: 2025-05-17 16:30:00

I work very hard to write clean concise comments. I will toil over them, read, re-read, and re-read again. Even still - I am terrible at catching my own spelling and grammar mistakes. I've recently gotten sick of other people spending time in code review fixing my mistakes. I know that I can do better, and I want to be better. So like any good developer - lets automate it!

This is my setup using pre-commit, aspell, and languagetool to automatically check spelling and grammar only in the changed lines of *.go and *.md files when committing code.

🛠 Tools Used

  • pre-commit: Git hook manager pipx install pre-commit
  • aspell: Spell checker brew install aspell
  • languagetool: Grammar checker brew install languagetool

These tools integrate cleanly into your local development workflow without linting untouched lines or scanning the entire codebase.

📁 Project Structure

Below is a simplified version of my repository layout:

your-repo/
├── .git/
├── .pre-commit-config.yaml  
├── hooks/           
│   ├── smart_spellcheck.sh
│   └── smart_grammar_check.sh
├── main.go
└── README.md

⚙️ .pre-commit-config.yaml

repos:
  - repo: local
    hooks:
      - id: smart-spellcheck
        name: Smart Spell Check (diff-only)
        entry: .hooks/smart_spellcheck.sh
        language: system
        pass_filenames: false

      - id: smart-grammar-check
        name: Smart Grammar Check (diff-only)
        entry: .hooks/smart_grammar_check.sh
        language: system
        pass_filenames: false

✏️ hooks/smart_spellcheck.sh

#!/bin/bash

# Get changed lines from staged files
FILES=$(git diff --cached --name-only --diff-filter=ACMR | grep -E '\.(go|md)$')

HAS_ERRORS=0

for FILE in $FILES; do
  if [ -f "$FILE" ]; then
    # Extract added or changed lines (without + at beginning)
    git diff --cached -U0 "$FILE" | \
      grep '^+[^+]' | \
      sed 's/^+//' > /tmp/spell_lines.txt

    if [ -s /tmp/spell_lines.txt ]; then
      echo "🔍 Checking spelling in changed lines of $FILE..."

      # Run aspell and collect misspelled words
      MISSPELLED=$(cat /tmp/spell_lines.txt | aspell list | sort | uniq)

      if [[ -n "$MISSPELLED" ]]; then
        echo "❌ Misspelled words in $FILE:"
        echo "$MISSPELLED"
        HAS_ERRORS=1
      fi
    fi
  fi
done

exit $HAS_ERRORS

📝 hooks/smart_grammar_check.sh

#!/bin/bash

if ! command -v languagetool >/dev/null 2>&1; then
  echo "⚠️  LanguageTool CLI not found. Skipping grammar check."
  exit 0
fi

FILES=$(git diff --cached --name-only --diff-filter=ACMR | grep -E '\.(go|md)$')

HAS_ERRORS=0

for FILE in $FILES; do
  if [ -f "$FILE" ]; then
    git diff --cached -U0 "$FILE" | \
     grep '^+[^+]' | \
     sed 's/^+//' > /tmp/grammar_lines.txt

    if [ -s /tmp/grammar_lines.txt ]; then
      echo "📝 Checking grammar in changed lines of $FILE..."
      languagetool --language en-US /tmp/grammar_lines.txt || HAS_ERRORS=1
    fi
  fi
done

exit $HAS_ERRORS

✅ Usage

To set it up:

  1. Install pre-commit: bash pip install pre-commit

  2. Install the hooks: bash pre-commit install

  3. Manually test: bash pre-commit run --all-files

✨ Result

Now when I try to commit changes, these hooks run automatically and alert me if I’ve introduced spelling or grammar mistakes — without touching the rest of the file.

It’s a simple setup, but it’s already helping keep my commits a little more polished. Hope it helps you too!