VS Code Extension

The Unfault VS Code extension shows you what your code means at runtime - where functions are called from, which routes they affect, and what safeguards exist in the call chain.

Installation

1. Open VS Code
2. Press Cmd+Shift+X (macOS) or Ctrl+Shift+X (Windows/Linux)
3. Search for “Unfault”
4. Click Install

The extension requires the Unfault CLI. If you haven’t installed it yet, follow the steps in /docs/installation, then authenticate:

unfault login

Note

The extension doesn’t have a separate sign-in flow. It uses the same credentials as the CLI (device login or UNFAULT_API_KEY).

What You’ll See

Code Lenses

Above each function, a code lens shows its runtime context:

uf: used by 3 places · reached by POST /api/checkout · worth a look

Click to open the Context sidebar with full details.

Context Sidebar

The sidebar (in Explorer) shows:

• Callers: Where this function is called from
• Routes: Which HTTP routes reach this function
• SLOs: Service level objectives linked to those routes
• Heads up (worth a look): Findings about the current function body (things to fix here)
• Upstream: Issues in code that calls into this function (things that can break you)
• Downstream: Issues in code you call from this function (things you rely on / can propagate)

The sidebar follows your cursor by default. Pin it to keep focus on a specific function.

File Centrality

The status bar shows how central the current file is:

• Hub icon: Many files depend on this one
• Star icon: Moderately central
• (no extra icon): Regular file

Click Show Files That Depend on This File (or use the Unfault menu) to see exactly what depends on the current file.

Configuration

Setting	Description	Default
unfault.executablePath	Path to CLI	unfault
unfault.fault.executablePath	Path to fault CLI	fault
unfault.fault.baseUrl	Base URL of the app under test	http://127.0.0.1:8000
unfault.codeLens.enabled	Show code lenses above functions	true
unfault.codeLens.clickToOpen	Click lens to open context sidebar	true
unfault.diagnostics.enabled	Show inline squiggles (calm mode off)	false
unfault.diagnostics.minSeverity	Minimum severity	high
unfault.trace.server	LSP trace level	off
unfault.verbose	Verbose logging	false

Tip

Diagnostics are disabled by default for a calmer experience. Enable them if you prefer inline feedback.

Commands

Access via Command Palette (Cmd+Shift+P) or click the status bar:

Command	Description
Open Context Sidebar	Open Unfault: Context in the Explorer sidebar
Run fault injection for current function	Open the fault injection panel for the current function
Generate fault scenarios for current function	Generate per-route scenario suites under tests/fault/ or test/fault/
Show Files That Depend on This File	List files that import this one
Show Unfault Output	View LSP logs for debugging
Open Unfault Settings	Jump to Unfault settings
Show Unfault Menu	Quick pick with all actions
Welcome & Setup	Welcome panel + auth help
Restart Unfault LSP Server	Restart the language server

Fault Injection

The Context sidebar includes a Fault Injection panel.

• If fault isn’t installed, the extension offers to run unfault addon install fault for you.
• Clicking Run starts fault run and opens a split terminal with a curl command targeting the proxy.
• Clicking Generate scenario file creates a repeatable scenario suite for the current route.

See /docs/guides/fault for details.

Supported Languages

• Python
• Go
• Rust
• TypeScript
• JavaScript

Troubleshooting

No code lenses appearing

1. Check that you’re in a supported file
2. Run unfault login in the terminal
3. Run Unfault: Restart Server
4. Check Output for errors

Extension slow on first open

The first analysis builds a semantic graph of your codebase. Subsequent interactions use the cache.

CLI not found

Set unfault.executablePath in settings to the full path to the unfault binary.

Learn More

For a detailed walkthrough of all features, see the VS Code Extension Tutorial.