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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered structurally. The description adds that the action must be one the avatar supports and that valid values come from list_actions, but says nothing about whether it interrupts an in-progress action, whether it blocks, or how errors surface.

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 core action and followed by the prerequisite. Nothing redundant or padded.

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 one-parameter, non-destructive action tool with full schema coverage and no output schema, the definition covers what it does and where to get valid inputs. Only edge-case behavior (invalid id, concurrent actions) is unaddressed.

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 schema already documents the single parameter as "Action id, or its 1-based index", so the description cannot add much value here. It does usefully indicate where valid values originate (list_actions), but gives no format or range detail beyond 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?

"Play one of the avatar's expressions, such as a wave" gives a specific verb (play) and resource (an avatar expression/action) with a concrete example, which is far more informative than the title alone. It does not explicitly contrast itself with siblings beyond pointing at list_actions, so it stops short of a 5.

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?

It gives an explicit prerequisite: call list_actions first to discover valid actions for this avatar. That is clear context for when to use it, but there is no guidance on when not to use it or what to do on failure/unknown ids.

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