Detect feature flag patterns in your codebase. Fallow identifies environment variable flags (process.env.FEATURE_*), SDK calls (LaunchDarkly, Statsig, Unleash, GrowthBook), and config object patterns (opt-in). Reports flag locations, detection confidence, and cross-references with dead code findings.
Use fallow flags --format json for structured output that agents and scripts can parse. Combine with --top N to focus on the most common flags.
Options Output Flag Description --top <N>Show only the top N flags -f, --format <FORMAT>Output format: human (default), json, sarif, compact, markdown, codeclimate -q, --quietSuppress progress output --explainAdd metric explanations. In JSON format, adds a _meta object with descriptions and docs links. --summaryPrint a one-line summary of flag counts at the end of the run. In JSON format, adds a summary counts object.
Scoping Flag Description -r, --root <PATH>Project root directory (default: current working directory) -c, --config <PATH>Path to config file (default: auto-detected) -w, --workspace <NAME>Scope output to a single workspace package --changed-since <REF>Only report flags in files changed since a git ref --productionProduction mode: exclude test/story/dev files
Flag Description --no-cacheDisable incremental caching (force full re-parse) --threads <N>Number of parser threads (default: available parallelism) --performanceShow pipeline timing breakdown
Flag Description --ciCI mode: equivalent to --format sarif --fail-on-issues --quiet --fail-on-issuesExit with code 1 if flags are found --sarif-file <PATH>Write SARIF output to a file (in addition to --format) --group-by <MODE>Group output by owner (CODEOWNERS), directory (first path component), or package (workspace package). See global flags .
Regression Flag Description --baseline <PATH>Compare against a previously saved baseline file --save-baseline <PATH>Save current results as a baseline file --fail-on-regressionFail if flag count increased beyond tolerance vs a regression baseline --tolerance <N>Allowed increase: "2%" (percentage) or "5" (absolute). Default: "0" --regression-baseline <PATH>Path to regression baseline file (default: .fallow/regression-baseline.json) --save-regression-baseline <PATH>Save current flag counts as a regression baseline
Detection categories Fallow detects three categories of feature flag patterns:
Category What it finds Examples Environment variable flags process.env.* checks used as feature gatesprocess.env.FEATURE_NEW_UI, process.env.ENABLE_DARK_MODESDK calls Feature flag SDK method calls from known providers LaunchDarkly variation(), Statsig checkGate(), Unleash isEnabled(), GrowthBook isOn() Config object patterns Object property lookups used as boolean guards (opt-in) config.featureX, settings.enableNewFlow
Each detected flag includes a confidence level indicating how certain fallow is that the pattern represents a feature flag.
Examples Basic analysis
CI integration
Scoping
# Detect all feature flags fallow flags # Show only the top 10 flags fallow flags --top 10
JSON output $ fallow flags --format json
{ "schema_version" : 3 , "version" : "2.27.0" , "elapsed_ms" : 116 , "feature_flags" : [], "total_flags" : 0 }
Key fields Field Type Description schema_versioninteger JSON schema version (currently 3) versionstring Fallow version that produced the output elapsed_msinteger Analysis duration in milliseconds feature_flagsarray Detected feature flag patterns total_flagsinteger Total number of detected flags
The feature_flags MCP tool wraps fallow flags --format json --quiet --explain:
{ "tool" : "feature_flags" , "arguments" : { "top" : 10 } }
The response always includes _meta explanatory metadata (the MCP wrapper enables --explain by default). Returns the same JSON envelope as the CLI.
See MCP integration for setup instructions.
See also
Dead code analysis Cross-references feature flags with dead code findings.
Global flags Flags available on every fallow command.
MCP integration Use fallow tools from AI coding agents.
