Set the tempo in BPM for a Strudel music session by writing the matching setcpm value, assuming one 4/4 bar per cycle.
Set BPM. Writes setcpm(bpm/4), assuming one bar of 4/4 per cycle.
| Name | Required | Description | Default |
|---|---|---|---|
| bpm | Yes | Tempo in BPM | |
| session_id | No | Optional session ID (#108). Omit to use default session. |
Changes observed during successful MCP inspections.
v4.0.0Input schema / properties / session_idAdded value: +{
+ "description": "Optional session ID (#108). Omit to use default session.",
+ "type": "string"
+}v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It does disclose one genuinely non-obvious behavior: the tool writes setcpm(bpm/4), assuming a bar of 4/4 per cycle. That conversion is invisible from the schema and valuable. However, it omits whether the change is global or session-scoped, whether it persists, and whether it affects currently playing audio, which are important for a mutation tool.
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 short sentences, front-loaded with the primary action, zero filler. Every clause carries information the caller could not get from structured fields.
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 mutation tool with no annotations and no output schema, the description is on the thin side. It explains the internal mapping but not the scope of effect, persistence, or whether the caller must supply session_id to target a specific session.
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%, so the baseline is 3. The description exceeds that by explaining the underlying transformation of the bpm value (bpm/4 into setcpm), giving the parameter meaning beyond 'Tempo in BPM.' The optional session_id is left to the schema.
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 opens with a specific verb and resource: 'Set BPM.' An agent immediately knows this changes the tempo. It doesn't differentiate itself from siblings like playback or compose, but 'Set BPM' is unambiguous enough that confusion is unlikely.
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?
There is no guidance on when to use this tool versus alternatives, no prerequisites, and no mention of when not to use it. The session_id parameter's behavior (default session fallback) is documented only in the schema, not the description.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.