Browserslist Validator

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name: browserslist-validator description: Validate .browserslistrc files and browserslist config in package.json for syntax errors, deprecated browsers, redundant queries, and best practices. Use when validating browserslist configuration, checking browser targeting, auditing frontend build configs, or linting .browserslistrc files.

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Browserslist Validator

Validate .browserslistrc files and browserslist entries in package.json for syntax errors, deprecated browsers, redundant queries, and best practices.

Commands

# Full validation (all rules)
python3 scripts/browserslist_validator.py validate .browserslistrc
Validate browserslist in package.json
python3 scripts/browserslist_validator.py validate package.json
Quick syntax-only check
python3 scripts/browserslist_validator.py check .browserslistrc
Estimate coverage
python3 scripts/browserslist_validator.py coverage .browserslistrc
Explain each query in human-readable form
python3 scripts/browserslist_validator.py explain .browserslistrc
JSON output
python3 scripts/browserslist_validator.py validate .browserslistrc --format json
One-line PASS/WARN/FAIL summary
python3 scripts/browserslist_validator.py validate .browserslistrc --format summary
Strict mode (warnings become errors)
python3 scripts/browserslist_validator.py validate .browserslistrc --strict
Target environment
python3 scripts/browserslist_validator.py validate .browserslistrc --env production

Rules (20)

| # | Category | Severity | Rule | |---|----------|----------|------| | S1 | Syntax | E | File not found or unreadable | | S2 | Syntax | E | Empty config (no queries) | | S3 | Syntax | E | Invalid query syntax / unknown browser name | | S4 | Syntax | W | Duplicate queries | | B1 | Browsers | W | Dead/deprecated browser (IE, Blackberry, etc.) | | B2 | Browsers | W | Browser with <0.01% global usage | | B3 | Browsers | E | Browser version does not exist (e.g. Chrome 999) | | B4 | Browsers | E | Unknown browser name | | Q1 | Queries | W | Redundant query (covered by broader query) | | Q2 | Queries | W | Conflicting queries (e.g. > 1% and < 0.5%) | | Q3 | Queries | E | not dead without any positive query | | Q4 | Queries | W | Empty result after not negation | | C1 | Coverage | W | Very low total coverage (<80%) | | C2 | Coverage | W | Very high coverage (>99.5%, may include dead browsers) | | C3 | Coverage | I | No mobile browser coverage hint | | C4 | Coverage | I | No country-specific override detected | | P1 | Best Practices | W | IE queries present (recommend dropping IE) | | P2 | Best Practices | W | Unreasonably old versions (last 20 versions) | | P3 | Best Practices | W | all query used (too broad) | | P4 | Best Practices | W | Version pinning instead of range (Chrome 90) |

Output Formats

text (default): Human-readable with [E]/[W]/[I] severity prefix

json: Machine-readable structured output

summary: Single-line PASS / WARN / FAIL

Exit Codes

0 — No errors

1 — Errors found (or warnings in --strict mode)

2 — File not found or parse error