tmodloader-mcp

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Is a session running?

status

Read-only

Check whether a tModLoader session is running and identify it, providing a safe read-only alternative to error-triggering commands.

Instructions

Whether a session is running, and what it is.

The only read-only way to ask. Without it an agent that lost track had to provoke an error to find out — launch fails when one exists, diag fails when one does not — so the cheapest question on the surface was the one that had to be asked by breaking something.

Reports what this server BELIEVES it started. It does not re-query the process table, so it cannot tell you a game was closed from outside; stop is what verifies against reality.

Input Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Output Schema

TableJSON Schema

Name	Required	Description	Default
`mode`	Yes
`port`	Yes
`world`	Yes
`joined`	Yes
`player`	Yes
`running`	Yes
`started_pids`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.6.3Sep 17, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Goes beyond the readOnlyHint and destructiveHint annotations by disclosing that it reports only what the server believes it started, does not re-query the process table, and cannot detect externally closed games. This is valuable behavioral context that prevents misinterpretation of results.

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

Conciseness4/5

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

The description is compact and front-loads the core purpose. The additional sentences about read-only superiority and limitation on external process changes are relevant, though the phrasing could be tightened without losing meaning.

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

Completeness5/5

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

Given zero parameters, rich annotations, and an output schema, the description is complete. It covers what the tool reports, its reliability limits, and how it fits among sibling tools, leaving no critical gap for agent invocation.

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

Parameters4/5

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

The tool has zero parameters, so there is no parameter semantics to convey. The baseline for zero-parameter tools is 4, and the description adds no unnecessary parameter information.

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

Purpose5/5

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

States exactly what the tool does: reports whether a session is running and what it is. It also distinguishes itself as 'the only read-only way to ask', contrasting with launch and diag, so an agent can tell it apart from siblings.

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

Usage Guidelines5/5

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

Explicitly explains when to use this tool: when an agent has lost track of session state and needs a read-only check. It contrasts with launch/diag, which fail depending on state, and notes that stop is needed to verify against reality, providing clear context on limitations.

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

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