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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral detail beyond that: it enumerates the returned fields and clarifies that invited-but-not-joined addresses appear as 'invited' only on the person's own circles.

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?

It is a single sentence front-loaded with the verb and resource, and every clause carries information. The clause about invited addresses is grammatically convoluted ('on the person's own, of each address invited...') and slightly slows parsing, but nothing is wasted.

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 no output schema, the description must carry the return-value burden, and it does by naming the fields returned. Nothing needs to be said about parameters or safety beyond the annotations, so the definition is essentially complete for a zero-param read tool.

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 and the schema is an empty object with additionalProperties=false, so there is nothing for the description to disambiguate. No parameter semantics are needed.

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 (list) and resource (circles) with an explicit scope: every circle the person owns or has joined. It also names the sibling circles_free_times_find and its different job, so an agent can separate the two without opening either 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?

The closing pointer to circles_free_times_find implies the boundary between browsing circles and finding a meeting time, but there is no explicit statement of when to call this tool versus circles_invite or the free-times tool. Usage is only implied, not stated.

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