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.
.fallowrc.json with autocomplete and validationBeyond 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:
fallow.health.enabled.client-server-leak, the tainted-sink CWE catalogue), framed as unverified candidates to verify, never confirmed vulnerabilities. Opt in with fallow.security.enabled.fallow audit.--workspace.Search for "fallow" in the VS Code extensions marketplace, or install from the command line:
code --install-extension fallow-rs.fallow-vscodeThe 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.
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.
Open any TypeScript or JavaScript project. Fallow activates automatically and starts analyzing. Diagnostics appear inline, and Code Lens annotations show above exports.
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.
Additional status-bar items, each independently toggleable:
fallow.health.statusBar)fallow.audit.statusBar.enabled)fallow.license.showStatusBar)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.
| 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.
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.
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.
.fallowrc.json files get autocomplete and validation powered by the published JSON schema. The extension registers this automatically, no extra setup needed.
| 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 |
| 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 3.15.0 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 |
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.