Browserslist Validator

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.

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

Commands

bash

# 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