FeatureLint
Feature flag hygiene analyzer that catches stale flags, SDK misuse, safety risks, and architecture problems before they reach production.
Emoji: flag Homepage: https://featurelint.pages.dev Product: featurelint Accent: #e84393
What It Does
FeatureLint statically analyzes your codebase for feature flag hygiene issues across six categories:
- Stale Flags (SF) — Detects hardcoded booleans, TODO-annotated flags, commented-out conditionals, and flags with past date references
- Flag Complexity (FC) — Finds nested flag conditions, excessive branching, flag entanglement, and missing caching in loops
- Flag Safety (FS) — Warns when flags gate authentication, payments, encryption, data deletion, or audit logging paths
- SDK Misuse (SM) — Catches missing default values, loop evaluations, multiple SDK initializations, and missing error handling
- Flag Lifecycle (FL) — Identifies flags without cleanup dates, abandoned experiments, 100% rollouts, and missing owner annotations
- Flag Architecture (FA) — Detects wrong-layer evaluation, service coupling, missing registries, and leaked server-side state
90 total patterns with POSIX ERE regex matching, severity levels, and actionable recommendations.
Installation
As a Git Hook (Lefthook)
# lefthook.yml
pre-commit:
commands:
featurelint:
glob: "*.{js,jsx,ts,tsx,py,rb,java,go,rs}"
run: bash path/to/featurelint/scripts/dispatcher.sh staged --severity errorDirect CLI Usage
# Scan a directory
bash scripts/dispatcher.sh scan ./src
# Scan with JSON output
bash scripts/dispatcher.sh scan --format json --output report.json ./src
# Analyze staged files
bash scripts/dispatcher.sh staged
# Single file analysis
bash scripts/dispatcher.sh file ./src/flags.ts
# Health check
bash scripts/dispatcher.sh healthTier System
| Tier | Patterns | Categories | Price |
|---|---|---|---|
| Free | 30 | Stale Flags + Flag Complexity | $0 |
| Pro | 60 | + Flag Safety + SDK Misuse | $9/month |
| Team | 90 | + Flag Lifecycle + Flag Architecture | $29/month |
Activate a tier by setting your license key:
export FEATURELINT_LICENSE_KEY="FEATURELINT-XXXX-XXXX-XXXX-XXXX"Commands
| Command | Description |
|---|---|
scan | Analyze a directory for feature flag issues |
file | Analyze a single file |
staged | Analyze git staged files (for pre-commit hooks) |
baseline | Create a baseline snapshot of current findings |
compare | Compare current findings against the baseline |
health | Run self-diagnostic health check |
version | Print version information |
help | Show usage and available options |
Options
| Flag | Description | Default |
|---|---|---|
-f, --format <fmt> | Output format: text, json, csv, markdown | text |
-o, --output <file> | Write report to file | (stdout) |
-s, --severity <lvl> | Minimum severity: error, warning, info, all | all |
-c, --category <cat> | Filter by category code | all |
-t, --tier <tier> | License tier: free, pro, team | free |
-j, --jobs <n> | Parallel scan workers | 4 |
-i, --include <glob> | Include files matching pattern | (all) |
-e, --exclude <regex> | Exclude files matching pattern | (none) |
-C, --context <n> | Context lines around findings | 2 |
--scan-hidden | Include hidden files and directories | false |
--warn-exit | Exit code 1 on warnings | false |
-v, --verbose | Increase verbosity (-vv for trace) | 0 |
-q, --quiet | Suppress non-essential output | false |
Environment Variables
| Variable | Description |
|---|---|
FEATURELINT_LICENSE_KEY | License key for tier activation |
FEATURELINT_TIER | Override tier directly |
FEATURELINT_FORMAT | Default output format |
FEATURELINT_SEVERITY | Default severity filter |
FEATURELINT_JOBS | Default parallel job count |
Output Formats
Text (default)
Human-readable terminal output with color-coded severity, file grouping, code context, and actionable fix recommendations.
JSON
Structured output for CI/CD integration. Includes metadata, summary counters, and a findings array with file, line, severity, check ID, description, and recommendation.
CSV
Spreadsheet-compatible output for tracking and reporting. One row per finding with all fields.
Markdown
Report template with summary tables, category breakdown, severity distribution, and a findings table. Uses the report.md.tmpl template when available.
Supported Languages
JavaScript, TypeScript, Python, Ruby, Java, Kotlin, Scala, Go, Rust, C#, F#, PHP, Swift, Dart, Vue, Svelte, Elixir, Clojure, Lua, R, YAML, JSON, TOML, XML, Terraform/HCL, and Shell.
Architecture
featurelint/
scripts/
dispatcher.sh # CLI entry point and argument parsing
analyzer.sh # Core analysis engine and output formatters
patterns.sh # 90 patterns across 6 categories
license.sh # License validation and tier gating
config/
lefthook.yml # Git hook configuration
templates/
report.md.tmpl # Markdown report template
SKILL.md # This fileExamples
CI/CD Integration (GitHub Actions)
- name: FeatureLint
run: |
bash featurelint/scripts/dispatcher.sh scan \
--format json \
--output featurelint-report.json \
--severity warning \
./srcBaseline Workflow
# Create initial baseline
bash scripts/dispatcher.sh baseline ./src
# After making changes, compare
bash scripts/dispatcher.sh compare ./srcPre-commit with Error-Only Blocking
bash scripts/dispatcher.sh staged --severity errorRequirements
- Bash 4.0 or later
- Standard POSIX utilities: grep, sed, awk, find, sort, uniq, wc, cut
- Optional: curl (for online license validation), git (for staged analysis)
License
Commercial software. Free tier available with 30 patterns. See https://featurelint.pages.dev for pricing and terms.