mcp-gopls – MCP server for Go (gopls)

A Model Context Protocol (MCP) server that lets AI assistants use Go’s LSP (gopls) for navigation, diagnostics, testing, coverage, and more.

> TL;DR: If you use Claude / Cursor / Copilot with Go, mcp-gopls gives the AI full LSP powers:
> go-to-definition, references, hover, completion, go test, coverage, go mod tidy, govulncheck, etc.

Overview

This MCP server helps AI assistants to:

- Use LSP to analyze Go workspaces
- Navigate to definitions, references, and workspace symbols
- Format, rename, and inspect code actions without leaving MCP
- Run Go tests, coverage, go mod tidy, govulncheck, and module graph commands with structured results
- Read workspace resources (overview + go.mod) and consume curated prompts

> Status: Actively developed – used in real projects.
> Tested with Go 1.25.x and gopls@latest.

Architecture

This project uses the mark3labs/mcp-go library to implement the Model Context Protocol. The MCP integration enables seamless communication between AI assistants and Go tools.

The server communicates with gopls, the official language server for Go, via the Language Server Protocol (LSP).

Features

- Configurable runtime: --workspace, --gopls-path, --log-level, --rpc-timeout, and --shutdown-timeout flags + env vars (MCP_GOPLS_*)
- Structured logging: Text/JSON logging with slog and optional file output
- Extended LSP surface: navigation, diagnostics, formatting, rename, code actions, hover, completion, workspace symbols
- Test & tooling helpers: coverage analysis, go test, go mod tidy, govulncheck, go mod graph
- MCP extras: resources (resource://workspace/overview, resource://workspace/go.mod) and prompts (summarize_diagnostics, refactor_plan)
- Progress streaming: long-running commands emit notifications/progress events so clients can surface status updates

Feature comparison: mcp-gopls vs built-in gopls MCP

As of gopls v0.20.0, the built-in MCP server exposes these tools:
go_context, go_diagnostics, go_file_context, go_file_diagnostics,
go_file_metadata, go_package_api, go_references, go_rename_symbol,
go_search, go_symbol_references, go_workspace, go_vulncheck.

| Feature / capability | mcp-gopls (this project) | Built-in gopls MCP |
|----------------------|----------------------------|----------------------|
| Go-to-definition | Yes (go_to_definition tool) | No dedicated MCP tool (not in tool list) |
| Find references | Yes (find_references) | Yes (go_references, go_symbol_references) |
| Diagnostics (file / workspace) | Yes (check_diagnostics) | Yes (go_diagnostics, go_file_diagnostics) |
| Hover information | Yes (get_hover_info) | No dedicated MCP tool (not in tool list) |
| Completion | Yes (get_completion) | No dedicated MCP tool (not in tool list) |
| Formatting | Yes (format_document) | No dedicated MCP tool (not in tool list) |
| Rename symbol | Yes (rename_symbol) | Yes (go_rename_symbol) |
| Code actions | Yes (list_code_actions) | No dedicated MCP tool (not in tool list) |
| Workspace symbol search | Yes (search_workspace_symbols) | Yes (go_search) |
| Package / workspace API/context tools | No dedicated MCP tool | Yes (go_package_api, go_file_context, go_file_metadata, go_workspace, go_context) |
| Run go test | Yes (run_go_test) | No MCP tool for running tests |
| Coverage analysis | Yes (analyze_coverage) | No MCP tool for coverage |
| go mod tidy | Yes (run_go_mod_tidy) | No MCP tool for go mod tidy |
| govulncheck | Yes (run_govulncheck) | Yes (go_vulncheck) |
| Module graph (go mod graph) | Yes (module_graph) | No MCP tool for module graph |
| Extra MCP resources | Yes (resource://workspace/overview, resource://workspace/go.mod) | Not documented as MCP resources |
| Custom MCP prompts | Yes (summarize_diagnostics, refactor_plan) | Not exposed as MCP prompts (only model instructions) |
| Model instructions shipped with server | No special mechanism (documented in README/docs) | Yes: gopls mcp -instructions prints usage workflows |

If you want full LSP-like editing + tooling from MCP (definition, hover, completion, format, rename, code actions, go test, coverage, go mod tidy, module graph), mcp-gopls is strictly richer.

If you mostly want read-only/introspective tools (diagnostics, symbol search, references, package API, workspace/file context, vulncheck) with no extra binary, the built-in gopls MCP is enough.

> Note: The built-in gopls MCP server is still marked experimental and its tool set may change over time. This comparison is accurate as of gopls v0.20.x.

Project Structure

.
├── cmd
│   └── mcp-gopls        # Application entry point
├── pkg
│   ├── lsp             # LSP client to communicate with gopls
│   │   ├── client      # LSP client implementation
│   │   └── protocol    # LSP protocol types and features
│   ├── server          # MCP server
│   └── tools           # MCP tools exposing LSP features

Installation

go install github.com/hloiseau/mcp-gopls/v2/cmd/mcp-gopls@latest

Quick Start

1. Install the server:

go install github.com/hloiseau/mcp-gopls/v2/cmd/mcp-gopls@latest

2. Verify it's on your $PATH:

mcp-gopls --help

3. Configure your AI client (see examples below for Cursor, Claude Desktop, or GitHub Copilot).

---

Docker / MCP Gateway

If you prefer to run mcp-gopls in a container (for Docker MCP Gateway or other containerized setups), use the official image.

Docker run

docker run --rm -i \
  -v /absolute/path/to/your/go/project:/workspace \
  ghcr.io/hloiseau/mcp-gopls:latest \
  --workspace /workspace

docker-mcp.yaml

Copy docs/docker-mcp.yaml, update the bind mount path, then run from that directory:

docker mcp gateway run

Tools catalog metadata

If your MCP catalog tooling requires a toolsUrl, use docs/tools.json as a static tool list.

Detailed Client Setup

> Note: All clients point to the same command:
> mcp-gopls --workspace /absolute/path/to/your/go/project
> The configuration format differs slightly per client, but the binary and arguments remain identical.

1. Connect from Cursor

1. Open Settings → MCP Servers → Edit JSON.
2. Add or update the mcp-gopls entry:

{
  "mcpServers": {
    "mcp-gopls": {
      "command": "mcp-gopls",
      "args": ["--workspace", "/absolute/path/to/your/go/project"],
      "env": {
        "MCP_GOPLS_LOG_LEVEL": "info"
      }
    }
  }
}

3. Run Developer: Reload Window so Cursor reconnects.
4. Open the Tools drawer in Cursor Chat and enable mcp-gopls.

2. Invoke the tools

| Tool / Prompt | Example request inside Cursor Chat |
|---------------|------------------------------------|
| go_to_definition | “Use go_to_definition on pkg/server/server.go:42.” |
| find_references | “Ask the tool for references to ServeStdio.” |
| check_diagnostics | “Request diagnostics for cmd/mcp-gopls/main.go.” |
| get_hover_info | “Call get_hover_info on pkg/tools/workspace.go:88.” |
| get_completion | “Trigger completions at pkg/server/server.go:55.” |
| format_document | “Run the formatter over pkg/tools/refactor.go.” |
| rename_symbol | “Rename clientFactory to newClientFactory via the tool.” |
| list_code_actions | “List code actions for pkg/server/server.go:80-90.” |
| search_workspace_symbols | “Search workspace symbols for NewWorkspaceConfig.” |
| analyze_coverage | “Run analyze_coverage for ./pkg/... with per-function stats.” |
| run_go_test | “Execute run_go_test on ./cmd/....” |
| run_go_mod_tidy | “Invoke run_go_mod_tidy to sync go.mod.” |
| run_govulncheck | “Run run_govulncheck and stream findings.” |
| module_graph | “Call module_graph to inspect dependencies.” |
| summarize_diagnostics | “Use the summarize_diagnostics prompt on the latest diagnostics.” |
| refactor_plan | “Feed refactor_plan the diagnostics JSON to plan fixes.” |

Client Setup Examples

Claude Desktop (macOS, Windows, Linux)

1. Install mcp-gopls and make sure it is on your $PATH.
2. Create or edit claude_desktop_config.json.
- macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
- Linux: ~/.config/Claude/claude_desktop_config.json
- Windows: %APPDATA%\Claude\claude_desktop_config.json
3. Add the server entry:

{
  "mcpServers": {
    "mcp-gopls": {
      "command": "mcp-gopls",
      "args": ["--workspace", "/absolute/path/to/your/go/project"],
      "env": {
        "MCP_GOPLS_LOG_LEVEL": "info"
      }
    }
  }
}

Restart Claude Desktop, open a chat, and ask it to connect to the mcp-gopls tool (Claude will show a “Tools” tab once the server is detected). Typical prompts include “list diagnostics for cmd/api/server.go” or “rename userService to accountService.”

Cursor IDE

In Cursor open Settings → MCP Servers → Edit JSON (this writes to ~/.cursor/config.json or the project-local override). Add:

{
  "mcpServers": {
    "mcp-gopls": {
      "command": "mcp-gopls",
      "args": ["--workspace", "/absolute/path/to/your/go/project"]
    }
  }
}

Reload Cursor (or run the Developer: Reload Window command) and the server will appear inside the “Tools” drawer. You can now ask Cursor Chat things like “run go test ./pkg/server with coverage” or “show hover info for pkg/tools/tests.go:42.”

GitHub Copilot (Agent Mode)

GitHub Copilot’s Agent Mode can talk to local MCP servers across VS Code, JetBrains IDEs, Eclipse, and Xcode (docs). To wire mcp-gopls in VS Code:

1. Update GitHub Copilot (requires VS Code 1.99+), opt into Agent Mode.
2. Create .vscode/mcp.json in your workspace (or edit the global file shown in the Copilot “Edit config” dialog).
3. Add:

{
  "servers": {
    "mcp-gopls": {
      "type": "stdio",
      "command": "mcp-gopls",
      "args": ["--workspace", "/absolute/path/to/your/go/project"],
      "env": {
        "MCP_GOPLS_LOG_LEVEL": "warn"
      }
    }
  }
}

4. Reload Agent Mode (toggle off/on) so Copilot discovers the new tool; the chat “Tools” picker will now expose every MCP action (run_go_test, run_govulncheck, etc.). JetBrains and other IDEs share the same JSON schema via their Copilot settings panel.

MCP Inspector / CLI testing

For quick smoke tests or demos you can use mark3labs/mcp-inspector:

npx -y @mark3labs/mcp-inspector \
  --command mcp-gopls \
  --args "--workspace" "/absolute/path/to/your/go/project"

The inspector lets you call each tool/resource/prompt manually, which is handy for debugging server configuration before wiring it into an AI assistant.

MCP Tools

| Tool | Description |
|------|-------------|
| go_to_definition | Navigate to the definition of a symbol |
| find_references | List all references for a symbol |
| check_diagnostics | Fetch cached diagnostics for a file |
| get_hover_info | Return hover markdown for a symbol |
| get_completion | Return completion labels at a position |
| format_document | Return formatting edits for an entire document |
| rename_symbol | Return workspace edits for a rename |
| list_code_actions | List available code actions for a range |
| search_workspace_symbols | Search workspace-wide symbols |
| analyze_coverage | Run go test with coverage + optional per-function report |
| run_go_test | Execute go test for a package/pattern |
| run_go_mod_tidy | Execute go mod tidy |
| run_govulncheck | Execute govulncheck ./... |
| module_graph | Return go mod graph output |

Progress Notifications

Long-running tools emit structured notifications/progress events so IDEs can show rich status indicators:

- Streaming progress (run_go_test, analyze_coverage, run_govulncheck, run_go_mod_tidy) forwards incremental log lines and percentage updates. Cursor displays these as a live log.
- Start/complete events only (go_to_definition, find_references, rename_symbol, etc.) fire a quick “started” event so the UI can show a spinner, followed by a completion payload with the final result.
- Each progress token is now namespaced (e.g., run_go_test/<rand>) to avoid “unknown token” errors when multiple tools run concurrently.

When integrating new tools, opt into streaming mode only if the underlying LSP/golang command produces meaningful interim output; otherwise stick to the lightweight start/complete flow to minimize noise.

Prompt Instructions

Both prompts are accessible from any MCP-aware client via the “Prompts” catalog.

summarize_diagnostics

- When to use: After check_diagnostics or run_go_test to turn raw diagnostics into actionable steps.
- Arguments: None. The server automatically reads the last diagnostics payload cached by the tools layer.
- Typical workflow: check_diagnostics → copy the returned array into the prompt input field (Cursor’s UI pastes it automatically when you select “Use last result”).

refactor_plan

- When to use: You already have a diagnostics JSON array and want a concise change checklist.
- Arguments: Requires a diagnostics object containing the raw Go diagnostics (the same payload returned by check_diagnostics).
- Example invocation payload:

{
  "diagnostics": [
    {
      "uri": "file:///path/to/pkg/tools/workspace.go",
      "range": {"start": {"line": 12, "character": 5}, "end": {"line": 12, "character": 25}},
      "severity": 1,
      "message": "unused variable testHelper"
    }
  ]
}

The prompt responds with a numbered set of refactor steps plus suggested validation commands (go test, analyze_coverage, etc.).

Configuration

The server supports various configuration options via command-line flags and environment variables:

Command-Line Flags

| Flag | Default | Description |
|-----------------------|---------|------------------------------------------------|
| --workspace | . | Absolute path to your Go project root |
| --gopls-path | gopls | Path to the gopls binary |
| --log-level | info | Log level (debug, info, warn, error) |
| --rpc-timeout | 30s | RPC timeout for LSP calls |
| --shutdown-timeout | 5s | Timeout for graceful shutdown |

Environment Variables

All flags can be set via environment variables with the MCP_GOPLS_ prefix:

| Environment Variable | Equivalent Flag | Description |
|---------------------------|-----------------------|------------------------------------------------|
| MCP_GOPLS_WORKSPACE | --workspace | Absolute path to your Go project root |
| MCP_GOPLS_GOPLS_PATH | --gopls-path | Path to the gopls binary |
| MCP_GOPLS_LOG_LEVEL | --log-level | Log level (debug, info, warn, error) |
| MCP_GOPLS_RPC_TIMEOUT | --rpc-timeout | RPC timeout for LSP calls (e.g., 30s, 1m) |
| MCP_GOPLS_SHUTDOWN_TIMEOUT | --shutdown-timeout | Timeout for graceful shutdown |

Command-line flags take precedence over environment variables.

Troubleshooting

- “column is beyond end of line” – gopls could not map the provided position. Confirm the file is saved and the position uses zero-based lines/columns; run go fmt to ensure tabs vs. spaces align with gopls expectations.
- “no hover information available” – the symbol might belong to a generated file or a module outside the configured workspace. Ensure the --workspace flag points to the module root and that go list ./... succeeds.
- “workspace not initialized” – the server did not finish its initial sync. Wait for the workspace initialized log line or restart mcp-gopls after deleting stale .gopls caches.
- run_govulncheck missing binary – the tool now falls back to go run golang.org/x/vuln/cmd/govulncheck@latest, but the machine still needs outbound network access. Install the binary manually if the fallback is blocked.

Usage Example

Using the server with AI assistants that support MCP:

```Markdown