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

Annotations already indicate a non-read-only, non-destructive mutation. The description adds useful context: it explains what gets added (plays with their outcomes and trivia marks) and notes that plays already on another account are left alone, clarifying overwrite behavior. It does not mention permissions or error handling, but adds value beyond annotations.

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?

The description is two sentences, front-loading the target user and action. It is efficient with little redundancy, though the parenthetical repetition of 'the play ids from this conversation' is slightly redundant with the schema.

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?

Given the tool's simplicity (one parameter), presence of annotations, and no output schema, the description provides sufficient context: it covers the trigger scenario, what is added, and a key constraint. It could mention idempotency or error cases, but those are largely covered by annotations.

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%: the single parameter play_ids is fully documented in the schema. The description repeats the parameter's source ('play ids from this conversation') but adds no new semantic details beyond what the schema provides, so baseline 3 is appropriate.

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 states a specific verb ('adds') and resource ('plays') and clarifies the scenario ('for a player who has just signed in', 'plays they made earlier without an account'). It does not explicitly name or contrast with sibling tools, but the purpose is clear enough to distinguish from typical play creation or retrieval tools.

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?

The description implies usage ('For a player who has just signed in') but does not specify when to use this tool versus alternatives (e.g., start_story, my_history) or any exclusions. The context is clear but lacks explicit routing guidance.

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