Codebase intelligence for JavaScript and TypeScript. Free static analysis reports quality, changed-code risk, cleanup opportunities, deterministic duplication, circular dependencies, complexity hotspots, architecture boundary violations, and feature flag patterns. An opt-in pinned local model discovers unverified semantically similar function candidates for agent or human review. Runtime coverage merges production execution data into the health report.
SkillScore86Maintained
Automatic
◆Coding pack
Last verified 10/9/2026
What it changes
Passed 18 of 21 test cases with the skill, and 7 of 21 without it.
Without skill33%
With skill86%
Checks it passed that the model alone missed
Passes --score to fallow health.
Includes the --coverage-gaps flag.
Executes the fallow health command.
and 14 more in the full report
11 fixed7 passed either way3 still failing0 broke2 errored
Pass-rate lift
+52 pp
Tokens
+285%
Agent turns
0%
Response time
-59%
Measured 10/9/2026v14 · latest is v1618 of 23 cases passed with skill · 21 comparable
Tokens, turns and time describe resource use, not a dollar price.
This benchmark measured an earlier version of the skill.
A newer attempt on gemini-3.8-flash on 10/18/2026 did not produce a publishable comparison (not comparable). The snapshot above is the previously measured run.
See it in action
One of 11 test cases the skill fixed. Same model, same prompt, with and without the skill.
1 of 11
Prompt
Our automated cleanup script flagged the npm package `lodash-es` as potentially unused. Before removing it from package.json, we want to trace all places where this dependency is referenced across the project. What command should be executed?
What was checked, without and with the skill
Checked
Without skill
With skill
Uses fallow dead-code with the --trace-dependency lodash-es flag.
Missed
Passed
case-10 · gemini-3.6-flash · 10/9/2026 · answers are capped and redacted
What's inside
The instructions your model reads when the skill loads.
SKILL.md414 lines8 files
Fallow: codebase intelligence for TypeScript and JavaScript
Fallow analyzes code and styles for changed-code risk, cleanup opportunities, circular dependencies, duplication, complexity hotspots, architecture boundary violations, design-system styling drift, feature flags, and opt-in security candidates. Runtime coverage merges production execution data into the same fallow health report for hot-path review and cold-path deletion confidence. A single local capture is available by default. Continuous or cloud runtime monitoring is optional.
When to Use
Find cleanup opportunities: unused files, exports, types, members, dependencies, or feature flags that guard unused exports.
Find functions that may implement the same intent despite different names, syntax, or control flow (fallow similar-code).
Check styling consistency, CSS dead surface, and design-token drift.
Audit changed code before a commit, PR, release, or refactor.
Set up CI quality gates, duplication thresholds, and regression baselines.
Auto-fix supported unused exports and dependencies after --dry-run.
Investigate why a specific export, dependency, file, or issue type was reported.
Surface local security candidates for an agent to verify (fallow security).
Find untested but runtime-reachable code (fallow health --coverage-gaps).
Rank complexity hotspots, owners, and refactoring targets (fallow health --hotspots --ownership --targets).
Review what fallow has surfaced over time (fallow impact).
Confirm exact TypeScript symbol use, affected tests, API leaks, or public type coupling when syntactic evidence is insufficient (--type-aware).
When NOT to Use
Runtime error analysis or debugging
Type checking (use tsc for that). Type-aware fallow consumes checker evidence for project-wide analysis but does not report compiler diagnostics.
Linting style or formatting issues (use ESLint, Biome, Prettier)
Verified security vulnerability scanning or SAST. fallow security surfaces local, deterministic security candidates for a downstream agent to verify; it does not prove exploitability. Use Snyk, CodeQL, or Semgrep for verified scanning, and an SCA tool for dependency CVEs.
Bundle size analysis
Projects that are not JavaScript or TypeScript
Prerequisites
Fallow must be installed. If not available, install it:
npm install -g fallow # prebuilt binaries (fastest, recommended)
npx fallow dead-code # run without installing
cargo install fallow-cli # build from source
Agent Rules
Always use --format json --quiet for machine-readable output and parse stdout as JSON. Compact JSON is the default; never depend on whitespace or add --pretty in agent pipelines. Keep stderr separate so diagnostics remain visible; never merge it into the JSON stream with 2>&1.