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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral facts beyond those: a hard cap of 20 results and soonest-first ordering. It omits whether the 20 cap is a truncation with no way to page past it, which is the one behavior an agent still has to guess.

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?

A single sentence front-loads what the tool returns, the cap and ordering, then the item fields, then the read-only note and the sibling redirect. Nothing is redundant and nothing needs re-reading.

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 zero-parameter read-only list with annotations and no output schema, the description supplies the essential shape of the return value (callId, who, number, when, reason) plus the ordering and limit. The remaining gap is what happens beyond 20 results, which matters given the explicit cap.

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, so there is nothing for the description to disambiguate and the baseline applies. The only semantic content is scope (scheduled, future, unplaced) rather than parameter meaning.

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 uses a specific scope statement: calls that are booked but not yet placed, with a definitive ordering and cap. It also explicitly distinguishes itself from list_calls ('past calls are in list_calls'), 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?

It names the closest alternative (list_calls for past calls) and the condition that selects it, which is real routing guidance. It does not mention when to pivot to cancel_scheduled_call or how it relates to list_bookings, so guidance is clear but not exhaustive.

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