How to fix npm ERR! code EJSONPARSE npm ERR! Duplicate key in npm

Copy your package.json contents into a JSON validator like JSONLint to identify the exact location of duplicate keys or syntax errors:

1. Go to https://jsonlint.com/
2. Paste your entire package.json
3. Click "Validate JSON"
4. Look for "Duplicate key" warnings in the results

Open package.json and search for common duplicated sections. Each of these should appear only once:

# Search for potential duplicates
grep -n '"dependencies"' package.json
grep -n '"devDependencies"' package.json
grep -n '"scripts"' package.json
grep -n '"name"' package.json

If any search returns multiple line numbers, you have duplicates to merge.

Check for and remove any leftover merge conflict markers:

# Search for conflict markers
grep -n "<<<<<<<\|=======\|>>>>>>>" package.json

If found, edit package.json to:
1. Remove all <<<<<<< lines
2. Remove all ======= lines
3. Remove all >>>>>>> lines
4. Keep only the correct version of conflicting code

Check for missing or trailing commas:

Missing comma (invalid):

{
  "name": "my-app"
  "version": "1.0.0"
}

Trailing comma (invalid in JSON):

{
  "name": "my-app",
  "version": "1.0.0",
}

Correct:

{
  "name": "my-app",
  "version": "1.0.0"
}

If you have two dependency sections, combine them into one:

Before (invalid):

{
  "dependencies": {
    "express": "^4.18.0"
  },
  "dependencies": {
    "lodash": "^4.17.0"
  }
}

After (valid):

{
  "dependencies": {
    "express": "^4.18.0",
    "lodash": "^4.17.0"
  }
}

After fixing the JSON, clear npm cache and reinstall:

# Clear npm cache
npm cache clean --force

# Remove existing artifacts
rm -rf node_modules package-lock.json

# Reinstall dependencies
npm install

If the file is too corrupted to fix manually, regenerate it:

# Backup current file
mv package.json package.json.bak

# Create fresh package.json
npm init -y

# Manually copy dependencies from backup
# Then reinstall
npm install