Playtest action

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

Goes well beyond the annotations: annotations only say it is a non-readonly, non-idempotent, non-destructive write, while the description discloses exactly what comes back (new screenshot, step number, steps left, SDK calls since last step, new console errors, ad requests, frame-change percentage), the serialization constraint, and the expiry failure mode. The heuristic that '0% often means the input did nothing' is genuinely useful diagnostic context an agent could not get from structured fields.

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?

Front-loaded with the verb and scope, then sequencing, then return payload, then failure/next-step — a logical order with no filler. The return-value sentence is a long comma-separated list, but since there is no output schema each item earns its place; only minor tightening (e.g. grouping the telemetry fields) is possible.

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 two-parameter interaction tool with no output schema, the description supplies the missing return-value contract, the failure modes, the concurrency/ordering model, and the follow-up tool. Nothing an agent needs in order to call this correctly, or to interpret the result, is absent.

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 description coverage is 100% and the description's action list ({type:...} variants) only restates what the oneOf branches and the action property description already document. No additional meaning such as coordinate origin conventions, key semantics, or sessionId lifecycle is added beyond the schema, so the baseline 3 applies.

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 ('Performs one action ... in a session started by gamealia_playtest') and enumerates the four action kinds (click, key, drag, wait). It also positions itself relative to siblings by naming the session-starting tool and the stop tool, so an agent can distinguish start, act, and stop without opening any schema.

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?

Gives explicit sequencing rules ('actions of one session run one at a time, in order'), an explicit failure condition ('fails if the session ended or expired'), and an explicit hand-off ('when steps run out, call gamealia_playtest_stop'). Both the when-to-use and the when-to-stop alternatives are stated rather than inferred.

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