unity_set_play_modeControl Unity Editor play mode: play, stop, pause, or unpause. Stop before structural scene edits because changes made while playing are lost.
Enter/exit play mode: play|stop|pause|unpause. Scene edits made while playing are lost on stop — prefer stopped for structural changes.
| Name | Required | Description | Default |
|---|---|---|---|
| action | Yes | Play-mode transition to perform |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so safety profile is partly covered. The description adds real value beyond that by warning that scene edits made during play are lost on stop, which is the key operational risk. It does not explain error behavior (e.g. what happens if play is already active) or that state persists across calls.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, zero padding, with the action enumeration front-loaded and the caveat immediately after. Every clause earns its place.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a single-enum mutation tool with annotations covering safety and no output schema, the description supplies the one thing structured data could not: the data-loss consequence of playing. It could go slightly further on error/state conditions, but nothing critical is missing.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and the single enum parameter is already fully documented in the schema. The description merely repeats the enum values verbatim (play|stop|pause|unpause) without adding syntax, side effects per value, or state requirements, so it is the baseline 3.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description names a specific verb (enter/exit) and resource (play mode) and enumerates the four transitions, so the action space is unambiguous. It does not explicitly distinguish itself from the read-side sibling unity_get_play_mode, so it falls short of the 5 bar.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
"prefer stopped for structural changes" gives explicit when-not guidance that steers the agent away from editing during play. It lacks any compatibility/prerequisite note (e.g. editor must be connected) and does not name a sibling as alternative, so it is clear but not complete.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.