lmstudio

LM Studio: start server

server_start

Idempotent

Starts the LM Studio API server on localhost, reusing the last port unless a specific port is provided for local model runtime access.

Instructions

Start the LM Studio API server on this machine (lms server start). Without port it reuses the last port. Listens on localhost only.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "server_start"
  }
}

Input Schema

Name	Required	Description	Default
`port`	No	Port to listen on. Default: the port used last time (usually 1234).

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Nov 11, 2026

TDQS

A3.8/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), and the description adds genuinely new context beyond them: the default port reuse behavior and the fact that it binds to localhost only, which is security-relevant. It stops short of describing the failure mode when a server is already active or what the call returns.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action and followed by the two behavioral facts that matter (port fallback and localhost binding). No filler or redundant framing.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-optional-parameter, no-output-schema tool, this is nearly complete: annotations carry the safety profile and the description supplies binding scope and port fallback. The only real gap is behavior when the server is already running, which matters given the idempotent hint.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the port parameter is fully documented in the schema with its default, so the description cannot add much. The line 'Without port it reuses the last port' restates what the schema already says, keeping this at the baseline 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Start the LM Studio API server on this machine') and even names the underlying CLI command ('lms server start'), so the action is unmistakable. It does not explicitly contrast itself with the sibling server_stop or server_status, so differentiation is left to the verb alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied: the tool starts the local API server, and the port sentence hints at the restart/reuse case. There is no explicit when-to-use or when-not-to-use guidance, and no mention of what happens if a server is already running.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.