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

Goes well beyond the annotations, which only say readOnly=false, destructive=false, idempotent=false. It discloses the real side effect (the run takes over the stage and the composition under test becomes the one on screen), explains why readOnly is false, notes buffering is tolerated, that any error ends the run, the ~20 s response window, and the incomplete reasons (tab hidden, interrupted, edited). It also reassures that source and props are unchanged.

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?

Purpose is front-loaded in the first sentence and the response shapes are enumerated compactly. The stage-takeover sentence partially restates the opening line, and the response-shape clauses are dense, but no sentence is wasted.

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?

There is no output schema, yet the description enumerates every response shape an agent must branch on (running/done/incomplete) with their fields. Combined with the side-effect disclosure and polling contract, an agent has everything needed to call and interpret it.

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 adds genuine meaning for 'id' by defining the continue-polling contract ('call again with the same id to keep waiting on the same run'), which the schema's terse 'Omit for the active one.' does not convey.

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?

States a specific verb and resource ('Plays a composition on the user's stage from the first frame to the last') and gives the outcome it reports ('whether it got to the end'). It also explicitly distinguishes itself from the sibling inspect_composition by noting it uses the same preview a person watches, which inspect_composition does not.

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?

Names the closest alternative (inspect_composition) and the axis on which they differ, and spells out the polling protocol: a {status:"running"} response means call again with the same id. What's missing is an explicit recommendation of when to prefer one over the other (e.g., static analysis vs. real rendering), so the choice is still partly inferential.

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