> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fallow.tools/llms.txt
> Use this file to discover all available pages before exploring further.
# VS Code extension
> Real-time codebase analysis in your editor: unused code, duplication, complexity hotspots, and boundary violations. Inline warnings, Code Lens reference counts, and one-click fixes.
The VS Code extension provides real-time diagnostics for unused code, duplication, complexity, and boundary violations, powered by the fallow LSP server.
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 all 15 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
## Installation
Search for "fallow" in the VS Code extensions marketplace, or install from the command line:
```bash theme={null}
code --install-extension fallow-rs.fallow-vscode
```
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.
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.
## 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
## Diagnostics
Every diagnostic includes a clickable **diagnostic code** (e.g., `unused-export`, `unresolved-import`) that opens the corresponding documentation page at [docs.fallow.tools](https://docs.fallow.tools).
### Related information
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 |
## 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.
## 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](https://raw.githubusercontent.com/fallow-rs/fallow/main/schema.json). The extension registers this automatically, no extra setup needed.
## Commands
| Command | Description |
| :--------------------------------------------------------- | :--------------------------------------- |
| **Fallow: Run Analysis** | Run full 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 |
| 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.issueTypes` | all | Which issue types to report |
| `fallow.duplication.threshold` | `5` | Minimum lines for duplication reporting |
| `fallow.duplication.mode` | `mild` | Duplication detection mode |
| `fallow.production` | `false` | Enable production mode |
| `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.trace.server` | `off` | LSP trace level for debugging |
### Adopting fallow on a legacy codebase
Use `fallow.changedSince` to keep existing issues hidden while flagging new ones in the Problems panel:
```bash theme={null}
git tag fallow-baseline
git push --tags
```
In `.vscode/settings.json`:
```json theme={null}
{
"fallow.changedSince": "fallow-baseline"
}
```
Commit `.vscode/settings.json` so the whole team sees the same scope. Pair the same tag with `fallow dead-code --changed-since fallow-baseline` in CI to enforce the same contract on PRs.
**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:
1. **Agents** run `fallow` from CLI or call MCP tools to verify their own output
2. **You in VS Code** see real-time diagnostics, review agent output, and spot issues as you code
3. **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.
## See also
How AI agents use fallow via CLI and MCP.
Add fallow to your CI pipeline.
All issue types shown in real time by the extension.