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spawn-mcp

by wfbcargo
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TypeScript
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spawn_client

Run client verbs like where, players, inputs, move, look, witness, screenshot, or run scripts against your joined game session to inspect and control a live body.

Instructions

Run any other verb of the packaged client against your standing body — spawn client <verb> …. Join first (spawn_client_join); these all act through that session.

The verbs the current client serves: where (your pose, world, place and the nearest objects — a sim read, no pixels), players (every body in the room and where it is), inputs (the world's declared actions — what a key actually does HERE, read it before sending any), move <x> <y> <z> or move --to <objectId> with --speed walk|run|teleport, look --at <objectId|x,y,z>, witness (the room as a picture), crossing (portals and slot census), screenshot, run <file> or run -e "<source>" (a play script: play.key / press / hold / release / walk / face / moveTo / where / players / entities / state / until).

The verb list belongs to the client the STACK serves, not to this server, so it can gain verbs without this tool changing — if one is not recognised, spawn_client verb:"--help" is not it; the client's own error names what it takes. --origin is refused: it would send your token to another stack.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
argsNoArguments, one array element each — never one joined string. `move 8 0 18 --speed walk` is ["8","0","18","--speed","walk"].
verbYesThe client verb: where, players, inputs, move, look, witness, crossing, screenshot, run, …
sessionNoSession name, so one machine can stand more than one body (default 'default'). Every verb takes it; a session self-expires at its ttl.
projectDirNoAbsolute path to the Spawn game project (.env). Defaults to SPAWN_PROJECT_DIR or the MCP process cwd.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv2.0.0

TDQS

A3.9/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and does disclose key behaviors: `--origin` is refused and why (token exfiltration), unknown verbs surface the client's own error, and the verb set can evolve independently of this tool. It is silent on permissions and return shapes, keeping it short of a 5.

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

Conciseness3/5

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

Purpose and prerequisite are front-loaded, but the middle is dense with long parentheticals enumerating verbs, and the closing note about `verb:"--help"` is convoluted. Most content earns its place, yet the prose is heavier than needed for a dispatcher.

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 passthrough dispatcher with no output schema and no annotations, the description covers prerequisites, verb semantics, session behavior (ttl via schema), and the security constraint. It does not describe return formats, but that gap is modest given the open-ended verb surface.

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?

Schema coverage is 100%, so a 3 is the baseline, but the description meaningfully enriches the `verb` parameter by explaining what each accepted value does (e.g. `where` is a sim read, no pixels; `inputs` describes key semantics HERE) and clarifies the arg-array convention that the schema also states.

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 action (dispatcher that runs any client verb against a standing body) and names the prerequisite sibling (spawn_client_join). It does not, however, differentiate itself from other exec-style siblings such as spawn_exec or spawn_play_console, leaving the agent to infer the boundary.

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

Usage Guidelines4/5

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

Gives explicit sequencing guidance ('Join first'), a routing hint to read `inputs` before sending any, and notes the verb list belongs to the client rather than this server. It stops short of stating when NOT to use this tool versus the narrower play/screenshot siblings.

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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