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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds a non-obvious behavioral limit the annotations cannot express: participants are counted but not listed, deliberately. It then names the mechanism that does expose membership, which prevents an agent from flailing at a dead end.

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 short sentences, front-loaded with what is returned, then the important negative constraint. Each sentence carries information, though the line-broken formatting is slightly airy for the amount of content.

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?

An output schema exists so return values needn't be spelled out, and the description still summarizes the payload shape plus the one thing the schema can't convey (membership opacity). Nothing needed to call this correctly is missing.

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 both parameters are richly documented in the schema itself (including the wrong-inbox not-found trap and the number_alias semantics). The description adds no parameter-level meaning beyond that, 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?

The description opens with a specific verb and resource ('Fetch a group') and enumerates what comes back: name, description, picture and settings. Combined with the required group_id, an agent can distinguish it from list_groups (many) and get_group_picture (one asset) 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?

It explicitly routes membership-change lookups to the `group.participants_*` events readable via `list_events`, which is genuine when-to-use-elsewhere guidance. What's missing is an explicit statement of when to prefer this over list_groups for a known group_id, though the required id makes that largely self-evident.

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