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

Annotations already declare readOnlyHint=true and destructiveHint=false, and 'Read-only' merely echoes them, but the description adds real behavioral context the annotations cannot: what is returned (name, id, model, playing style) and that the id is a foreign key for other tools. It stops short of covering ordering, empty-state behavior, or whether the list is paginated, so it is strong rather than exhaustive.

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?

Three front-loaded sentences, each carrying distinct information: definition, call ordering, and return/usage contract. Minor waste in repeating 'Read-only' when readOnlyHint already encodes it, and the phrasing 'saved poker characters this account owns' is slightly redundant with 'user's stars', but nothing is 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?

With zero parameters, no output schema, and annotations covering the safety profile, the remaining burden is to explain the return contract and session ordering — both are present. Nothing an agent needs in order to call this correctly is missing, and the downstream star_id handoff prevents the most likely follow-up misuse.

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?

The tool takes zero parameters, so the baseline is 4; the description correctly adds no per-parameter noise. Its discussion of star_id refers to downstream tools' parameters, which is helpful routing information but not compensation for this tool's 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?

States a specific verb and resource ('List the user's stars') and immediately disambiguates the domain term by defining stars as 'the saved poker characters this account owns'. It also names the sibling it must not be confused with (create_star) and the consumers of its output (join_table, playbook), so an agent can distinguish it from every sibling without opening a 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 timing and ordering rules: 'Call it first in a session, and always before `create_star`', with the consequence spelled out ('so the user does not end up with a duplicate'). It also tells the agent what to do with the result (pass id as star_id to join_table or playbook), which is genuine when-and-how guidance rather than a restatement of purpose.

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