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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint, openWorldHint). The description adds a real behavioral detail beyond them: results are scoped to what is 'visible to the caller,' i.e., access-controlled visibility. Because an output schema exists, it need not explain the return payload.

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?

Two compact sentences with no waste, though the ordering is slightly inverted: the usage trigger ('When you need...') leads before the core purpose is stated, and the title 'List Circles' already implies the second sentence.

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 low-complexity, parameterless-by-default list tool with full annotation coverage and an output schema, nearly everything an agent needs is present. The only soft spot is the ambiguous 'members / policies' clause, which could leave an agent unsure whether related data comes back from this call.

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?

There is a single parameter with 100% schema coverage, so the schema already documents the 'limit' parameter and its default of 50. The description adds nothing about pagination or limit behavior, so this is the baseline 3.

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 second sentence ('Lists circles visible to the caller') gives a specific verb and resource that clearly distinguishes it from the create/update/archive/invites siblings. The first sentence muddies the purpose slightly by implying the tool also surfaces 'members' and 'circle policies,' which aren't obviously part of a circles-list operation.

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 opens with a when-to-use trigger ('When you need the human's circles...'), which is genuine usage context, but it names no alternative tool and gives no exclusions or prerequisites. The 'members / policies' phrasing is broad enough to be ambiguous about when a sibling like circles.members.remove context is actually needed.

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