A testing workbench for MCP (Model Context Protocol) servers. Inspect a server's tool surface, call tools, price the context-token budget of a tool set, and bench a real model against it — all from the command line.

This npm package is a thin installer/launcher: on install it downloads the right prebuilt jig binary for your platform from GitHub Releases, verifies its SHA-256 checksum, and puts it on your PATH. The heavy lifting is done by the native Rust binary — see the main repository for full documentation.

Use

No install needed — run it straight with npx the same way you run MCP servers:

npx @shodh/jig inspect --stdio "npx -y @modelcontextprotocol/server-everything"

Or install it globally:

npm install -g @shodh/jig
jig inspect --stdio "npx -y some-mcp-server"

Common commands:

jig inspect --stdio "<server cmd>"                 # handshake + list tools/resources/prompts
jig call    --stdio "<server cmd>" --tool <name> --args '{"...":"..."}'
jig budget  --stdio "<server cmd>" --model gpt-4o --model claude-sonnet
jig bench   --stdio "<server cmd>" --task "book a table for two"

jig also speaks remote MCP over Streamable HTTP via --http <url> (with repeatable --header "Authorization: Bearer …"). Run jig --help for the full surface.

Exit codes are meaningful and forwarded faithfully by the launcher: 0 success · 1 a jig-level failure (transport/protocol/usage) · 2 a tool call that the server reported as isError: true.

Supported platforms

Prebuilt binaries are published for:

OS	Arch	Node `platform/arch`	Release target
Windows	x64	`win32/x64`	`x86_64-pc-windows-msvc`
macOS (Intel)	x64	`darwin/x64`	`x86_64-apple-darwin`
macOS (Apple)	arm64	`darwin/arm64`	`aarch64-apple-darwin`
Linux	x64	`linux/x64`	`x86_64-unknown-linux-musl`

On any other platform/arch the installer fails with a clear message pointing you at the cargo build path:

cargo install --git https://github.com/Shodh-Labs/jig jig-cli

Security: checksum verification

Every download is verified before it is trusted. The installer fetches the release's SHA256SUMS alongside the archive and computes the SHA-256 of the downloaded archive in memory; if it does not match the published digest, the install aborts and nothing is extracted or written. On Windows the archive is parsed entirely in-process (no shelling out), so the verified bytes never touch disk before being trusted.

Publishing to npm uses npm provenance, so you can trace the published package back to the exact GitHub Actions run and commit that produced it.

Environment overrides

Variable	Effect
`JIG_BINARY_PATH`	Use this local binary verbatim and skip all network access. For CI, air-gapped, and testing.
`JIG_DOWNLOAD_BASE`	Download from this base URL instead of GitHub Releases. Layout: `{base}/v{version}/{asset}`.

Examples:

# Use a binary you built or vendored yourself; no download happens.
JIG_BINARY_PATH=/path/to/jig npm install -g @shodh/jig

# Pull binaries from an internal mirror that mirrors the GitHub Releases layout.
JIG_DOWNLOAD_BASE=https://mirror.internal.example/jig npm install -g @shodh/jig

Behind a proxy

Node's built-in HTTP client does not honor HTTPS_PROXY/HTTP_PROXY, and this installer keeps a zero-dependency footprint, so it connects directly. If a proxy is configured the installer warns and continues; if the direct connection then fails, download the release archive manually and point JIG_BINARY_PATH at the extracted binary, or install via cargo (above).

How it works / offline notes

Windows archives are .zip; the single binary entry is extracted with a small in-process zip reader (Node has zlib but no zip reader) — no external tools, no temp files.
macOS/Linux archives are .tar.gz; the binary is streamed out with the system tar (always present on the supported unix targets). There is no pure-JS tar fallback by design.