Make GitHub Copilot dramatically better at Rust.

Instead of typing cargo commands into a terminal and squinting at the text output, Copilot calls Cargo as a set of structured tools — getting precise diagnostics with exact file paths and line numbers it can act on directly, streaming progress while builds run, and one-click application of Clippy and rustc fix suggestions.

Install, reload, run /cargo-mcp:setup once per repo. That's it.

Platforms: Pre-built binaries ship for Windows x64 and arm64. Linux/macOS users should build from source.

What you get

Precise diagnostics — JSON-shaped errors with exact file paths and line numbers, instead of best-effort parsing of compiler text.
Streaming build progress — long builds report live status in the chat panel; a one-line summary collapses into history when finished.
Reviewable fix suggestions — machine-applicable Clippy and rustc suggestions appear in a checkbox dialog you can accept selectively.
Automatic retry on Windows file-in-use errors — transient antivirus or file-indexer collisions in target\ no longer derail multi-step tasks.
Toolchain transparency — the cargo_diagnostic tool reports exactly which cargo and rustc will be invoked, and why.
cargo-nextest support — cargo_nextest_run and cargo_nextest_list are wired up alongside cargo_test for per-test process isolation, built-in retries, and filter expressions (install instructions are emitted automatically when the plugin is missing).
Zero MCP config — the extension bundles the server and registers it with VS Code automatically. No mcp.json to edit.

Screenshots

Note: The images below are placeholders shipped with the initial release; real screenshots will replace them in a follow-up.



Streaming build progress in the chat panel.	Clippy suggestions in a reviewable checkbox dialog.

Precise diagnostics with exact file paths and line numbers.

Quick start

Install this extension.
Reload VS Code so the MCP server registers and slash commands appear.
Open Copilot Chat in Agent mode and run:
```
/cargo-mcp:setup
```
This adds a short instruction block to your repository's .github/copilot-instructions.md (or equivalent) telling Copilot to prefer the MCP tools over running cargo in a terminal. Commit the change and Copilot will use the tools for every future session in that repository.

Why the setup step? Tool descriptions are only visible to Copilot after it has decided how to carry out a task. A repository instruction file is loaded before that decision, so it reliably intercepts the choice before Copilot reaches for a terminal.

Tools

Tool	Purpose
`cargo_check`	Fast compile-error checking
`cargo_build`	Full compilation with diagnostics
`cargo_test`	Run tests; structured results
`cargo_clippy`	Lints with reviewable fix suggestions
`cargo_fmt` / `cargo_fmt_check`	Apply / verify formatting
`cargo_doc`	Build documentation
`cargo_tree`	Dependency tree
`cargo_metadata`	Workspace / package / dependency graph
`cargo_clean`	Remove build artefacts
`cargo_update`	Update `Cargo.lock`
`cargo_fix`	Apply machine-applicable fixes in bulk
`cargo_add` / `cargo_remove`	Dependency management
`cargo_publish`	Publish to crates.io (`dry_run` recommended first)
`cargo_nextest_run` / `cargo_nextest_list`	Run / enumerate tests via cargo-nextest (requires the `cargo-nextest` plugin)
`cargo_diagnostic`	Report which `cargo`/`rustc` will be invoked
`cargo_setup`	Return the canonical Copilot-instruction text

Full tool reference and parameter docs →

Trust & transparency

Installing a VS Code extension that ships a native binary is a real trust decision. Here's what's in the box and what mitigates the risk:

Written in Rust. The MCP server is a single Rust crate. Rust's memory-safety guarantees apply to all of it by default — buffer overflows, use-after-free, and data races in safe code are compile-time errors, not runtime exploits.
All unsafe is in one ~600-line submodule. The production binary's entire unsafe surface area lives in src/rm/ — a safe wrapper around the Windows Restart Manager API that powers the "which process is holding this file open?" diagnostic. Every unsafe block is a single Win32 call, wraps a documented API (RmStartSession / RmRegisterResources / RmGetList / RmEndSession and FormatMessageW / LocalFree), uses Microsoft's official windows-sys bindings (so there are no hand-rolled FFI declarations to verify), and carries a // SAFETY: comment naming the precondition. Session handles are released by an RAII guard so leaks and double-closes are not possible from safe code. The rest of the crate — argument parsing, cargo invocation, output handling, MCP protocol — is unsafe-free.
Releases are built entirely in GitHub Actions. Every published VSIX is produced from a tagged commit by the publish-extension workflow on GitHub-hosted runners — cargo build --release --locked for the bundled binary, then vsce package --no-dependencies, then Marketplace upload. The publish step is gated by a required-reviewer environment, so no commit reaches the Marketplace without a human approval after CI has built the artifacts. No developer machine ever touches the published bits.
Reproducible inputs. Both the Rust build (--locked) and the extension's npm install (npm ci against a checked-in package-lock.json) refuse to use any dependency version not pinned in the lockfiles.
No telemetry, no network calls beyond the ones cargo itself initiates when you invoke cargo_update, cargo_add, cargo_publish, etc.
The source is the source. The full repository, including all CI configuration, is at github.com/MikeGrier/cargo-mcp-rs. You can read every line, audit the unsafe blocks, and reproduce the build yourself.

Requirements

VS Code 1.101 or later
GitHub Copilot Chat with Agent mode enabled
Rust toolchain (cargo on PATH)
rustup — optional but strongly recommended if your repo uses rust-toolchain.toml. Without rustup, the toolchain file has no effect on any cargo invocation (this is a property of cargo itself, not specific to this extension).
cargo clippy and cargo fmt components installed if you want cargo_clippy / cargo_fmt

Settings

Setting	Default	Description
`cargo-mcp.elicitationMode`	`always-skip`	How to handle machine-applicable fix suggestions: `prompt`, `always-accept`, or `always-skip`.
`cargo-mcp.test.timeoutSecs`	`30`	Default wall-clock timeout in seconds for `cargo_test` runs. Covers only test execution — the clock starts when compilation and linking finish, so a slow build never trips it. Routed by the server to whichever knob matches the call: in unfiltered mode it defaults `timeout_secs` (overall wall-clock); in `test_filter` mode it defaults `per_test_timeout_secs` (per-test idle watchdog that resets on every libtest boundary), so hung-test protection is on by default in filter mode while a long matched run can still complete. Explicit `timeout_secs` / `per_test_timeout_secs` arguments always override this default. Set to `0` to disable the server-provided default. In `test_filter` mode, `0` (or an absent setting) still leaves a hard-coded 30-second per-test fallback in place so hung-test protection stays on; the only way to fully disable per-test protection for a call is an explicit `per_test_timeout_secs: 0` in the tool arguments.
`cargo-mcp.retry.onBusy`	`true`	Retry idempotent cargo invocations (`check`, `build`, `test`, `clippy`, `fmt`, `doc`, `tree`, `clean`, `metadata`) when they fail with a transient Windows file-locking error (`(os error 32)` sharing violation, `(os error 5)` access denied, being used by another process). These usually clear themselves within a fraction of a second once an antivirus, file indexer, or stray process releases the handle.
`cargo-mcp.retry.delayMs`	`500`	Delay between retry attempts, in milliseconds.
`cargo-mcp.retry.maxAttempts`	`3`	Maximum total attempts (initial try + retries).
`cargo-mcp.binaryPath`	(bundled)	Override the path to the `cargo-mcp` binary. Intended for development against a locally-built server.

Commands

cargo-mcp: Open Copilot setup chat — opens Copilot Chat with the setup prompt pre-filled.
cargo-mcp: Copy bundled server binary path — copies the bundled cargo-mcp binary path to the clipboard.
cargo-mcp: Show bundled server version — displays the bundled server version.