Inspecting a server with mcp dev

The MCP Inspector is a developer tool that connects to a server and shows its tools, resources and prompts, so you see what a server offers before any model does.

Last updated: 28 Sep, 2026 · MCP 2.2

You have built a server and called it from code. Before you connect a server to a host, you want to see what it exposes and try a tool by hand. MCP gives you two ways to do that: the Inspector web app launched by mcp dev, and the same listing calls from your own code.

The mcp dev command

mcp dev loads your server file and opens the Inspector, a local web app, in your browser. There you pick a tool, fill its arguments in a form, and read the result, with no host and no model involved. It needs the [cli] extra from the setup lesson and Node.js for the web app, so it is shown here as a command rather than captured output.

mcp dev shop.py

The page lists the server's tools, resources and prompts, and lets you call each one and watch the JSON-RPC messages go back and forth. It is the MCP counterpart of a run transcript: a window on what the server did.

Listing a server in code

The same four listing calls the Inspector makes are methods on the in-memory client. They run keyless, with no browser, so they belong in a small script you can keep.

tools = await client.list_tools()
resources = await client.list_resources()
templates = await client.list_resource_templates()
prompts = await client.list_prompts()

Inspecting the shop server in code

Run the four listings against the server as it stands after the last lesson: one tool, with no resources or prompts yet.

import asyncio

from mcp import Client
from shop import mcp


async def main():
    async with Client(mcp) as client:
        tools = await client.list_tools()
        print("tools:", [t.name for t in tools.tools])
        resources = await client.list_resources()
        print("resources:", [str(r.uri) for r in resources.resources])
        templates = await client.list_resource_templates()
        print("templates:", [t.uri_template for t in templates.resource_templates])
        prompts = await client.list_prompts()
        print("prompts:", [p.name for p in prompts.prompts])


asyncio.run(main())

What the listing shows now

• tools holds lookup_order, the one tool registered so far.
• resources and templates are empty until Resources: data an application loads and Resource templates: one function for many URIs add them.
• prompts is empty until Prompts: templates a user picks adds one. Run this script again after those lessons and the same four lines fill in.

Reading one tool's schema

Listing gives more than names. Each tool carries its description and input schema, the same fields a host reads to decide when and how to call it.

import asyncio

from mcp import Client
from shop import mcp


async def main():
    async with Client(mcp) as client:
        tools = await client.list_tools()
        for tool in tools.tools:
            print(tool.name, "-", tool.description)
            print("  args:", list(tool.input_schema["properties"]))


asyncio.run(main())

The Inspector vs listing in code

When to inspect a server

• Right after adding a tool, to confirm its name, description and arguments are what you meant.
• Before connecting a server to Claude Code or another host, to see what that host will be offered.
• When a host cannot see a tool, to check whether the server lists it at all.

Related

• Previous: Client: connecting and calling a tool
• Next: Tool arguments: descriptions, limits and choices
• Reference: MCP Inspector