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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint, so safety is covered. The description adds genuinely non-obvious behavior: secret key values are never returned, and identity must be established via id/name instead. That is meaningful context beyond the annotations.

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 tight sentences with the core purpose front-loaded, then the auth constraint, then the secret-handling caveat. The trailing 'GET /{calendarKey}/keys' is slightly redundant but harmless.

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 carries the return-value burden and does so by naming the four exposed fields, plus auth requirements and the secret-omission behavior. Pagination is covered by the schema, so nothing essential is missing for a correct 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?

Schema description coverage is 100% and all four filters (type, limit, offset, name_contains) are documented in the schema, including the pagination contract via next_offset. The description adds no filter syntax or format detail, so the baseline of 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?

States a specific verb and resource ('List the calendar's access keys') and immediately disambiguates what an access key is ('sharing links and user accesses'), plus enumerates the returned fields (name, role, active state, per-sub-calendar permission). No sibling tool covers this resource, so the agent can place it instantly.

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?

Provides a concrete prerequisite ('Needs a key with admin permission') and a usage rule for telling links apart ('use the id and name'). It does not name alternatives or exclusions, but there are no overlapping siblings in this tool set, so the missing piece is low-impact.

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