Environment variables

Override fallow defaults with environment variables like FALLOW_FORMAT and FALLOW_QUIET. Useful for CI pipelines, editor integrations, and MCP.

Fallow reads a small set of environment variables to override default behavior. These are useful for CI pipelines, editor integrations, and the MCP server.

Variable	Description	Values
FALLOW_FORMAT	Default output format	human, json, sarif, compact, markdown, codeclimate, gitlab-codequality, pr-comment-github, pr-comment-gitlab, review-github, review-gitlab, badge
FALLOW_QUIET	Suppress progress output	1 or true
FALLOW_BIN	Path to the fallow binary	Any valid path
FALLOW_EXTENDS_TIMEOUT_SECS	Timeout for fetching URL extends	Seconds (default: 5)
FALLOW_PRODUCTION	Global production-mode override for every analysis	true/false/1/0/yes/no/on/off
FALLOW_PRODUCTION_DEAD_CODE	Per-analysis production override for dead-code (combined runs and fallow audit)	Same values as FALLOW_PRODUCTION
FALLOW_PRODUCTION_HEALTH	Per-analysis production override for health	Same values as FALLOW_PRODUCTION
FALLOW_PRODUCTION_DUPES	Per-analysis production override for duplication	Same values as FALLOW_PRODUCTION
FALLOW_REVIEW_GUIDANCE	Add collapsed “What to do” blocks to review-github / review-gitlab inline comments	1, true, yes, on
FALLOW_SUMMARY_SCOPE	Sticky PR/MR summary scope for pr-comment-github / pr-comment-gitlab. all keeps project-level dependency/catalog/override findings outside the diff; diff applies the diff filter to those findings too. Inline review comments are unaffected	all (default), diff
FALLOW_AUDIT_CACHE_MAX_AGE_DAYS	Max age of persistent reusable fallow audit base-snapshot worktree caches	Whole days (default 30; 0 disables)
FALLOW_TELEMETRY	Opt-in telemetry mode, off by default (see what it collects)	off/on/inspect (plus 0/1/true/false/disabled/enabled/debug/log)
FALLOW_TELEMETRY_DISABLED	Admin/fleet telemetry kill switch (top precedence)	1, true, yes, on
FALLOW_TELEMETRY_DEBUG	Forces inspect mode (outranks FALLOW_TELEMETRY)	1, true, yes, on
DO_NOT_TRACK	Honored as a top-precedence telemetry kill switch	1, true, yes, on
FALLOW_AGENT_SOURCE	Declare the calling agent for telemetry classification (never enables telemetry)	codex, claude_code, cursor, copilot, opencode, aider, roo, windsurf, gemini (aliases gemini_cli/antigravity), cline, continue, zed, goose, other_known, unknown, none

FALLOW_FORMAT

Set the default output format so you don’t need to pass --format every time.

export FALLOW_FORMAT=json
fallow dead-code   # Outputs JSON without --format flag

The --format CLI flag takes precedence over FALLOW_FORMAT when both are set.

FALLOW_QUIET

Suppress progress bars and status messages. Useful in CI environments or when piping output.

export FALLOW_QUIET=1
fallow dead-code   # No progress output, only results

Equivalent to passing --quiet on every command.

FALLOW_BIN

Path to the fallow binary. Used by the MCP server (fallow-mcp) to locate the fallow CLI.

export FALLOW_BIN=/usr/local/bin/fallow
fallow-mcp   # MCP server uses the specified binary

Defaults to fallow on PATH when not set.

FALLOW_EXTENDS_TIMEOUT_SECS

Timeout in seconds for fetching remote configs via https:// URLs in the extends field.

export FALLOW_EXTENDS_TIMEOUT_SECS=10
fallow dead-code   # URL extends have 10s to respond

Defaults to 5 seconds when not set.

FALLOW_CACHE_MAX_SIZE

Maximum on-disk extraction cache (.fallow/cache.bin) size in megabytes. Wins over the cache.maxSizeMb config field when both are set.

export FALLOW_CACHE_MAX_SIZE=64
fallow dead-code   # cache capped at 64 MB

Defaults to 256 (MB) when not set. The cache triggers LRU eviction when its serialized size crosses 80% of the cap and evicts down to 60%. Intended for CI runners with disk quotas; local dev machines on full-size disks rarely need to touch this knob.

--no-cache disables the cache entirely; this env var is then irrelevant.

FALLOW_AUDIT_CACHE_MAX_AGE_DAYS

Maximum age (in whole days, since last reuse or fresh create) of a persistent reusable fallow audit base-snapshot worktree cache. Older entries are removed at the top of the next fallow audit invocation. Wins over the audit.cacheMaxAgeDays config field when both are set.

export FALLOW_AUDIT_CACHE_MAX_AGE_DAYS=7
fallow audit --base origin/main   # caches older than 7 days are reclaimed

Defaults to 30 days when not set. Setting the value to 0 disables the GC entirely (escape hatch for CI runners that prune /tmp out-of-band). Invalid values (non-integer, negative) silently fall back to the config field / default; a typo in a runner env var does not fail audits.

The sweep runs once per fallow audit invocation, walks git-registered worktrees only (not raw /tmp content), and never removes a cache entry that another in-flight fallow audit is using (per-entry kernel flock(2) guard). On reclaim, fallow writes a single fallow: reclaimed N stale base-snapshot caches line to stderr (unless --quiet is set) so the disk-space recovery is observable.

FALLOW_PRODUCTION and per-analysis overrides

FALLOW_PRODUCTION mirrors the --production CLI flag and turns production mode on for every analysis. The per-analysis vars (FALLOW_PRODUCTION_DEAD_CODE, FALLOW_PRODUCTION_HEALTH, FALLOW_PRODUCTION_DUPES) target a single analysis when running bare combined mode (fallow with no subcommand) or fallow audit.

# Run combined mode with production-only health, full-tree dead-code and dupes
export FALLOW_PRODUCTION_HEALTH=true
fallow --format json --quiet

Precedence (highest to lowest):

1. CLI flags (--production, --production-{dead-code,health,dupes})
2. Per-analysis env var (FALLOW_PRODUCTION_HEALTH, etc.)
3. Global env var (FALLOW_PRODUCTION)
4. Config (production: true legacy form, or production: { health: true, ... } per-analysis form)

Per-analysis env beats global env, so FALLOW_PRODUCTION=false FALLOW_PRODUCTION_HEALTH=true runs health in production mode and the other analyses in non-production mode. Single-subcommand runs (e.g. fallow health) still respect FALLOW_PRODUCTION_HEALTH even though the per-analysis CLI flag is rejected with a subcommand: pass --production or set the per-analysis env var.

Set FALLOW_FORMAT=json and FALLOW_QUIET=1 in CI pipelines for clean machine-readable output.

See also

MCP server

AI agent integration using the Model Context Protocol.

fallow dead-code

Full CLI reference including all output format options.