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

readOnlyHint=true already tells the agent this is a safe read. The description's main addition is the start/end coupling constraint and the mention of returned fields, but the coupling rule is already restated in the schema, and there is no pagination, rate-limit, or result-shape context beyond a bare field list.

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 plus an endpoint reference, with the returned-shape and filtering constraints front-loaded and no filler. The 'FUB: GET /v1/appointments' trailer is marginal value but not padding.

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 simple read-only list tool with full schema coverage and no output schema, the description covers return fields and filter combinations adequately. It leaves gaps on pagination behavior and on how this list differs from fub_list_events, both of which an agent working across sibling tools would benefit from.

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%, so all six parameters are already documented with their constraints (limit range, offset deep-paging hint, ISO-8601 formats). The description only restates the filtering semantics at a high level, adding nothing beyond the schema, so 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 names the resource (calendar appointments) and the fields it returns (invitees, type, outcome), which is more specific than the bare title 'List appointments'. It does not, however, distinguish itself from the sibling fub_list_events, which an agent could plausibly confuse with calendar appointments.

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 states the three supported filter modes (person, user, start+end window) and the coupling rule that start and end must be used together. That implies usage but gives no explicit when-to-use or when-not-to-use guidance, and names no alternative tool for related queries.

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