pkgsite-mcp

MCP tools for looking up current Go module and package information from the official pkg.go.dev/v1beta API.

Use it when you want a coding agent to answer Go dependency questions with structured pkg.go.dev data instead of guessing from model memory, scraping HTML, or cloning repositories.

Hosted server

MCP endpoint:

https://pkgsite-mcp.fly.dev/mcp

The hosted server is read-only and does not require an API key.

Add to Codex

Codex supports streamable HTTP MCP servers with codex mcp add --url:

codex mcp add pkgsite --url https://pkgsite-mcp.fly.dev/mcp

Equivalent ~/.codex/config.toml entry:

[mcp_servers.pkgsite]
url = "https://pkgsite-mcp.fly.dev/mcp"

Add to Claude Code

Claude Code supports HTTP MCP servers with claude mcp add --transport http:

claude mcp add --transport http pkgsite https://pkgsite-mcp.fly.dev/mcp

Use --scope user if you want it available outside the current project:

claude mcp add --scope user --transport http pkgsite https://pkgsite-mcp.fly.dev/mcp

Equivalent JSON shape:

{
  "mcpServers": {
    "pkgsite": {
      "type": "http",
      "url": "https://pkgsite-mcp.fly.dev/mcp"
    }
  }
}

Add to Cursor

Cursor supports URL-based MCP servers in mcp.json. Add this to your Cursor MCP configuration:

{
  "mcpServers": {
    "pkgsite": {
      "url": "https://pkgsite-mcp.fly.dev/mcp"
    }
  }
}

Cursor also accepts an explicit HTTP type in contexts that use its typed MCP server config:

{
  "mcpServers": {
    "pkgsite": {
      "type": "http",
      "url": "https://pkgsite-mcp.fly.dev/mcp"
    }
  }
}

What agents can ask

pkgsite-mcp exposes read-only tools for common Go package research:

• Search packages and symbols on pkg.go.dev.
• Fetch module metadata, README text, licenses, versions, and contained packages.
• Fetch package metadata and exported symbols.
• Check which packages import a package.
• Check vulnerabilities for a module or package path.
• Load short built-in guides that help agents use the tools precisely.
• Run pkgsite_explain for a compact combined lookup of a module or package.

Examples of useful prompts after adding the MCP server:

Use pkgsite to check the latest github.com/jackc/pgx/v5 version and summarize notable package symbols.

Use pkgsite to inspect vulnerabilities for golang.org/x/crypto and tell me whether this repo should upgrade.

Use pkgsite to compare the exported APIs of github.com/redis/go-redis/v9 packages relevant to clients and pipelines.

Local development

Build the binary:

just build

Run over stdio:

.cache/bin/pkgsite-mcp serve --transport stdio

Run over streamable HTTP:

.cache/bin/pkgsite-mcp serve --transport http --addr :8080

Local MCP endpoint:

http://localhost:8080/mcp

Health endpoint:

http://localhost:8080/health

Start optional Redis for local caching and rate limiting:

just up
just serve-http

Use just down to stop Redis and just logs to follow Redis logs.

Local MCP config

For clients that only support stdio, point them at a local binary:

{
  "mcpServers": {
    "pkgsite": {
      "command": "/absolute/path/to/pkgsite-mcp/.cache/bin/pkgsite-mcp",
      "args": ["serve", "--transport", "stdio"]
    }
  }
}

For HTTP-capable clients, use:

http://localhost:8080/mcp

Configuration

PKGSITE_BASE_URL=https://pkg.go.dev/v1beta
KV_REDIS_URL=redis://localhost:9736/0
KV_REDIS_POOL_SIZE=4
KV_REDIS_MIN_IDLE_CONNS=2
KV_REDIS_MAX_IDLE_CONNS=4
KV_REDIS_MAX_ACTIVE_CONNS=8
KV_REDIS_POOL_TIMEOUT=250ms
KV_REDIS_DIAL_TIMEOUT=1s
KV_REDIS_READ_TIMEOUT=750ms
KV_REDIS_WRITE_TIMEOUT=750ms
KV_REDIS_CONN_MAX_IDLE_TIME=10m
KV_REDIS_DISABLE_IDENTITY=true
PKGSITE_HTTP_TIMEOUT=10s
PKGSITE_CACHE_DISABLED=false
RATE_LIMIT_ENABLED=true
RATE_LIMIT_REQUESTS=120
RATE_LIMIT_WINDOW=1m
SENTRY_DSN=
O11Y_SERVICE_NAME=pkgsite-mcp
O11Y_ENVIRONMENT=
O11Y_FLUSH_TIMEOUT=2s
O11Y_TRACES_SAMPLE_RATE=1.0
O11Y_ENABLE_LOGS=true
O11Y_ENABLE_METRICS=true

Redis is optional. Without KV_REDIS_URL, requests go directly to pkg.go.dev and IP rate limiting is disabled. When Redis is configured, it backs both pkg.go.dev response caching and fixed-window IP rate limiting for /mcp.

Sentry is optional. Without SENTRY_DSN, observability calls stay no-op.