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

With no annotations, the description carries the behavioral burden. It discloses a meaningful security behavior ('an identifier is NEVER returned — SEC-PM-006') and the authentication prerequisite, which are not visible in the schema. The read-only nature is only implied by 'Get' rather than stated, but the added privacy and access context is substantial.

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 compact and front-loaded: the core purpose and return shape appear in the first sentence, followed by a tight access note. Every sentence contributes either behavioral disclosure or routing guidance; there is no filler.

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 single-parameter lookup with no output schema, the description explains what is returned, highlights a key privacy constraint, and states the authentication prerequisite. It does not specify error behavior or the exact member data shape, but the essential calling context is covered.

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 one parameter, id, and schema description coverage is 100%: the schema already documents it as a Circle ID with a regex pattern. The description adds only 'by ID', which maps directly to the schema, so it does not meaningfully extend parameter semantics beyond the baseline.

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 'Get a Circle by ID', naming a specific verb and resource, and then specifies what is returned (members and per-member channel presence booleans). It is clearly distinguishable from siblings like list_circles, create_circle, update_circle, and delete_circle.

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 gives a clear access context: a Proof account is required, the client must be authenticated first, and 'start_login does NOT open this tool' is an explicit when-not. It does not explicitly name alternatives like list_circles for discovering the ID, so it falls short of full usage routing.

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