fallow: codebase intelligence for TypeScript and JavaScript

The VS Code extension provides real-time diagnostics for unused code, duplication, complexity, and boundary violations, powered by the fallow LSP server, plus sidebar views and status-bar surfaces for project health, security candidates, runtime coverage, the changed-files audit verdict, monorepo workspace scoping, and license management.

Code Lens shows reference counts above each export. Click to peek all usages. Exports with zero references stand out immediately.

Features

Real-time diagnostics for dead-code issue types, updated via LSP without running a separate CLI process
Code Lens with reference counts above each export (click to peek references)
Hover information with export usage counts, unused status, and duplicate block locations
Quick-fix code actions to remove unused exports or delete unused files
Refactor actions to extract duplicates into shared functions
Tree views in the sidebar with per-category icons, issue count badge, and welcome view
Status bar with color-coded severity, rich tooltip breakdown, and command links
Diagnostic documentation links: click any diagnostic code to open its docs page
Related information: circular dependencies, duplicate exports, and code duplication diagnostics link to all related files
Fix preview with a searchable Quick Pick for reviewing and navigating fixes
JSON schema for .fallowrc.json with autocomplete and validation
Auto-download of the LSP binary
Getting Started walkthrough on first install

Codebase intelligence surfaces

Beyond the real-time LSP diagnostics above, the extension surfaces the rest of fallow’s analysis, each as its own opt-in sidebar view or status-bar item:

Health view (sidebar): project health score and grade, top complexity findings, and hotspot / refactoring candidates, from a separate lazy run. Opt out with fallow.health.enabled.
Security Candidates view (sidebar): local security candidates (client-server-leak, the tainted-sink CWE catalogue), framed as unverified candidates to verify, never confirmed vulnerabilities. Opt in with fallow.security.enabled.
Runtime Coverage view (sidebar): hot paths and cleanup candidates (safe-to-delete / review-required) from a loaded coverage capture.
Audit verdict (status bar): a pass / warn / fail signal for your current change set, mirroring fallow audit.
License management: activate, view status, refresh, and deactivate a Fallow license without leaving the editor.
Monorepo workspace scope (status bar): a picker to scope sidebar analysis (and the Health, Security, and Audit surfaces) to a single package, forwarding --workspace.

Installation

Install the extension

Search for “fallow” in the VS Code extensions marketplace, or install from the command line:

code --install-extension fallow-rs.fallow-vscode

Binary resolution

The extension finds binaries automatically. It checks the fallow.lspPath setting first, then node_modules/.bin/ for a local devDependency (pnpm add -D fallow), then system PATH, or auto-downloads from GitHub releases.

Getting Started walkthrough

On first install, a walkthrough opens automatically with four steps: Run Analysis, Explore Results, Fix Issues, and Configure Rules. Each step links directly to the relevant command. You can reopen it from the Command Palette at any time.

Start coding

Open any TypeScript or JavaScript project. Fallow activates automatically and starts analyzing. Diagnostics appear inline, and Code Lens annotations show above exports.

Status bar

The status bar shows the current issue count and duplication percentage. It updates in real time as the LSP server completes analysis via a custom fallow/analysisComplete notification. No separate CLI process needed.

Color-coded background: red when unresolved imports are present (errors), yellow when other issues exist (warnings), default when the project is clean
Rich tooltip: hover to see a per-category breakdown of all issues (unused files, exports, dependencies, circular dependencies, clone groups, etc.)
Command links in tooltip: Run Analysis, Auto-Fix, and Show Output are one click away

Additional status-bar items, each independently toggleable:

Health score segment with the project grade (toggle with fallow.health.statusBar)
Audit verdict for the current change set: pass / warn / fail, color-coded, with a gating-candidate count (toggle with fallow.audit.statusBar.enabled)
License indicator showing the active license state (toggle with fallow.license.showStatusBar)
Workspace scope picker showing the package analysis is scoped to in a monorepo (hidden on single-package projects)

Diagnostics

Every diagnostic includes a clickable diagnostic code (e.g., unused-export, unresolved-import) that opens the corresponding documentation page at docs.fallow.tools. Some diagnostics include related information that links to other files involved in the issue. Click a related location in the Problems panel to jump directly to it.

Circular dependencies: each file in the cycle chain is listed as a related location, so you can trace the full cycle
Duplicate exports: links to the other files that export the same name
Code duplication: links to all other instances of the duplicated block

Severity levels

Issue type	Severity	Appearance
Unresolved imports	Error (red)	Red underline
Unused files, dependencies, circular deps, duplicate exports	Warning (yellow)	Yellow underline
Unused exports, types, enum/class members	Hint	Faded text (unnecessary tag)
Code duplication	Information (blue)	Blue underline
Security candidates (opt-in)	Information (blue)	Blue underline

Security candidate diagnostics are off by default and distinct from the Security Candidates sidebar view. They appear in the editor gutter only when you raise the security-sink or security-client-server-leak rule to warn or error in your fallow config, framed as unverified candidates to verify (advisory, never a red error). The hover leads with the confidence signals and points to fallow security --file for the full trace; a quick-fix dismisses the candidate.

Tree views

The sidebar groups issues by type and duplicates by clone family. Each category uses a distinct icon for quick scanning:

Category	Icon
Unused files	File
Unused exports	Method
Unused types	Interface
Unused dependencies	Package
Unused enum members	Enum member
Unresolved imports	Error
Circular dependencies	Sync
Duplicate exports	Files

A badge on the sidebar icon shows the total issue count at a glance. When no analysis has been run yet, a welcome view appears with a “Run Analysis” button. Clicking any item in the tree opens the file at the exact line and column.

Additional views

The sidebar also hosts three opt-in views beyond unused code and duplicates:

View	Shows
Health	Project health score and grade, top complexity findings, and hotspot / refactoring candidates
Security Candidates	Local security candidates (`client-server-leak`, tainted-sink CWE catalogue), framed as unverified candidates to verify
Runtime Coverage	Hot paths and cleanup candidates (safe-to-delete / review-required) from a loaded coverage capture

Fix preview

Fallow: Preview Fixes (Dry Run) opens a searchable Quick Pick listing each available fix with its type and file location. Select an item to navigate to it in the editor, or choose Apply all fixes at the bottom to apply everything at once. After applying fixes, the extension automatically saves modified files, restarts the LSP server, and re-runs analysis so diagnostics update immediately.

Config autocomplete

.fallowrc.json files get autocomplete and validation powered by the published JSON schema. The extension registers this automatically, no extra setup needed.

Commands

Command	Description
Fallow: Run Analysis	Run full analysis
Fallow: Set Baseline at HEAD	Create or use the local `fallow-baseline` tag at `HEAD`, set `fallow.changedSince`, and refresh analysis
Fallow: Auto-Fix (unexport unused, remove unused deps)	Apply auto-fixes
Fallow: Preview Fixes (Dry Run)	Preview fixes in a searchable Quick Pick
Fallow: Restart Language Server	Restart the language server
Fallow: Show Output Channel	Open the LSP output channel
Fallow: Reload Health	Re-run the Health view analysis
Fallow: Scan for Security Candidates	Populate the Security Candidates view
Fallow: Select Workspace Scope…	Scope analysis to one monorepo package
Fallow: Clear Workspace Scope (Analyze All)	Remove the workspace scope
Fallow: Load Runtime Coverage	Point the Runtime Coverage view at a capture
Fallow: Reload Runtime Coverage	Re-read the current coverage capture
Fallow: Clear Runtime Coverage	Clear the loaded coverage
Fallow: Audit Changed Files	Compute the pass/warn/fail audit verdict for the current changes
Fallow: Activate License	Activate a license (paste a token, load a file, or start a trial)
Fallow: Show License Status	Show the current license state
Fallow: Refresh License	Refresh the license from the server
Fallow: Deactivate License	Deactivate the license on this machine

Extension settings

Setting	Default	Description
`fallow.lspPath`	-	Path to `fallow-lsp` binary (highest priority, overrides local `node_modules/.bin`, PATH, and auto-download)
`fallow.autoDownload`	`true`	Auto-download the LSP binary when not found locally or in PATH
`fallow.typeAware.enabled`	`false`	Add exact TypeScript symbol evidence to Fallow’s project-wide analysis. Does not surface compiler diagnostics or generic typed lint rules. Requires Fallow 3.9.2 or newer.
`fallow.typeAware.projects`	`[]`	Optional tsconfig paths for type-aware analysis. Relative paths resolve from the workspace root.
`fallow.typeAware.require`	`"best-effort"`	Keep incomplete semantic evidence advisory, or choose `"complete"` to fail after emitting the conservative result.
`fallow.issueTypes`	all	Which issue types to report
`fallow.duplication.threshold`	`0`	Maximum allowed duplication percentage before the analysis is marked as failing (`0` = no limit)
`fallow.duplication.minTokens`	`50`	Minimum token count for a clone before it can be reported as duplicated code
`fallow.duplication.minLines`	`5`	Minimum line count for a clone before it can be reported as duplicated code
`fallow.duplication.minOccurrences`	`2`	Minimum occurrences before a clone group is reported (raise to `3`+ to skip pair-only clones)
`fallow.duplication.mode`	`mild`	Duplication detection mode
`fallow.duplication.near`	`false`	Include function-scoped near-miss clones with small structural edits alongside exact clones. Requires Fallow 3.14.0 or newer.
`fallow.duplication.skipLocal`	`false`	Only report duplicate code that appears across different directories
`fallow.duplication.crossLanguage`	`false`	Compare TypeScript and JavaScript files after stripping TypeScript type annotations
`fallow.duplication.ignoreImports`	`true`	Exclude module wiring from duplicate-code detection. Enabled by default for ES imports, re-export declarations, and top-level static `require()` binding declarations; set to `false` to count module wiring as clone candidates again.
`fallow.production`	`"auto"`	Production mode for the sidebar tree and the editor diagnostics (they stay in sync). `"auto"` defers to the project config, `"on"` forces production mode on, `"off"` forces it off even if the project config enables it. Editor-only; CLI and CI always report every finding.
`fallow.changedSince`	`""`	Git ref to scope diagnostics and the sidebar to files changed since that ref (mirrors `--changed-since`). Tag a baseline commit (e.g. `fallow-baseline`) and set this to the tag to enforce “no new issues going forward” while ignoring pre-existing findings.
`fallow.diagnostics.severity`	`"warning"`	Render Fallow editor diagnostics as `warning`, `information`, or `hint`. `hint` keeps findings available without squiggles. Editor-only; CLI and CI output are unchanged.
`fallow.diagnostics.mutedCategories`	`[]`	Team-shareable baseline of Fallow diagnostic category codes to hide in the editor, such as `code-duplication` or `stale-suppression`. Commit in `.vscode/settings.json`; local mutes can still hide more or show a baseline-hidden category. Editor-only; CLI and CI output are unchanged.
`fallow.workspace`	`""`	Scope sidebar analysis (and the Health, Security, and Audit surfaces) to a single monorepo package by name. Empty = analyze the whole project. Forwarded as `--workspace`.
`fallow.health.enabled`	`true`	Show the Health view (score and grade, complexity findings, hotspot and refactoring candidates)
`fallow.health.hotspots`	`true`	Include git churn hotspots in the Health view (walks git history; disable to skip that cost)
`fallow.health.topFindings`	`20`	Maximum number of complexity findings shown in the Health view
`fallow.health.statusBar`	`true`	Show the project health score and grade in the status bar
`fallow.health.inlineComplexity`	`true`	Show a compact complexity lens (`N cyc, N cog`) above functions that exceed Fallow Health thresholds. Click the lens to expand or collapse that function’s per-line `+N` breakdown
`fallow.complexity.breakdownEnabled`	`true`	Master switch for the complexity breakdown (lens, per-line markers, and hovers) shown in the editor after the Health view runs
`fallow.complexity.afterText`	`false`	Always show the dim per-line `+N` token for every complex function, instead of only the function you expand (via its lens) or select in the Health view. Hovering always shows the breakdown regardless
`fallow.complexity.decorationCap`	`200`	Number of top complexity findings fetched for editor decorations, independent of `fallow.health.topFindings`
`fallow.security.enabled`	`false`	Surface local security candidates (`client-server-leak`, tainted-sink CWE catalogue) in the Security Candidates view. Unverified candidates to verify, not confirmed vulnerabilities.
`fallow.audit.gate`	`new-only`	Which findings affect the audit verdict shown in the editor (mirrors `fallow audit --gate`)
`fallow.audit.statusBar.enabled`	`true`	Show the audit verdict (pass/warn/fail) for the current change set in the status bar
`fallow.audit.runOnSave`	`false`	Re-run the audit verdict when a JS/TS file is saved (off by default)
`fallow.coverage.capturePath`	`""`	Path to a local runtime-coverage capture (file or directory) for the Runtime Coverage view
`fallow.coverage.top`	`0`	Show only the top N hot paths and findings in the Runtime Coverage view (`0` = all)
`fallow.license.showStatusBar`	`true`	Show a Fallow license indicator in the status bar
`fallow.license.refreshOnStartup`	`false`	Probe license status once when the extension activates (off by default; no network on startup)
`fallow.trace.server`	`off`	LSP trace level for debugging

Adopting fallow on a legacy codebase

Run Fallow: Set Baseline at HEAD from the Command Palette to keep existing issues hidden while flagging new ones. The command creates the local lightweight fallow-baseline tag at the current commit, writes fallow.changedSince to the workspace settings, and refreshes analysis. It confirms before replacing another effective baseline setting, refuses multi-root workspaces, and never moves an existing tag or pushes to a remote. To share the baseline with your team, push that tag explicitly and commit the generated .vscode/settings.json change:

git push origin refs/tags/fallow-baseline
git add .vscode/settings.json
git commit -m "chore: set fallow baseline"

Pair the same tag with fallow dead-code --changed-since fallow-baseline in CI to enforce the same contract on pull requests.

Shallow clone footgun. actions/checkout@v4 defaults to fetch-depth: 1 and GitLab CI defaults to GIT_DEPTH: 50. If your baseline tag predates that fetch boundary, --changed-since and fallow.changedSince silently fall back to full scope (the LSP logs a warning to the Fallow output channel). Set fetch-depth: 0 on actions/checkout (or GIT_DEPTH: 0 in GitLab CI) when you use a long-lived baseline tag.

Part of the three tracks

VS Code is one of three ways to use fallow:

Agents run fallow from CLI or call MCP tools to verify their own output
You in VS Code see real-time diagnostics, review agent output, and spot issues as you code
CI catches the rest, so nothing lands in main without passing fallow

The same analysis engine and the same config power all three, so results are identical across CLI, VS Code, and CI.

Agent integration

How AI agents use fallow via CLI and MCP.

CI integration

Add fallow to your CI pipeline.

Analysis areas

All issue types shown in real time by the extension.

Getting Started

Analysis

Cloud

Configuration

Integrations

Explanations

Frameworks

Migration

VS Code extension

Features

Codebase intelligence surfaces

Installation

Status bar

Diagnostics

Severity levels

Tree views

Additional views

Fix preview

Config autocomplete

Commands

Adopting fallow on a legacy codebase

Part of the three tracks

See also

Agent integration

CI integration

Analysis areas

​Features

​Codebase intelligence surfaces

​Installation

​Status bar

​Diagnostics

​Related information

​Severity levels

​Tree views

​Additional views

​Fix preview

​Config autocomplete

​Commands

​Adopting fallow on a legacy codebase

​Part of the three tracks

​See also

Agent integration

CI integration

Analysis areas

Features

Codebase intelligence surfaces

Installation

Status bar

Diagnostics

Related information

Severity levels

Tree views

Additional views

Fix preview

Config autocomplete

Commands

Adopting fallow on a legacy codebase

Part of the three tracks

See also