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

Annotations already declare readOnly, idempotent, open-world and non-destructive, so the safety profile is covered. The description adds real behavioral context beyond them: the 30-day window, that n counts only arrivals with a recorded arrival time, that a late rule with a minute threshold is applied, and that cancelled flights are included. It does not state behavior for unknown flight numbers or data freshness, which keeps it from a 5.

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 sentences, no filler, and the core purpose is front-loaded before the return-value inventory. The second sentence is a dense comma list, but every listed item is a distinct output field the agent would otherwise have to discover by calling.

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 burden of explaining returns and does so thoroughly (on-time/late/cancelled counts, n, window, late rule, link). Combined with full schema coverage and annotations, an agent has everything needed to call it correctly.

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 coverage is 100% and the single 'number' parameter already documents the required format with an example (BA117). The description adds nothing about parameter meaning, so the schema does the work and the 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 a specific resource and measurement ('How often a flight has been late over the last 30 days') plus the returned metrics, which is enough to distinguish it from a status-style sibling. It does not explicitly name the current-status alternative, so differentiation relies on the agent inferring that 'history' means past performance rather than live status.

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?

Usage is only implied: the 30-day window and 'history' framing suggest this is for reliability/lateness questions rather than immediate flight status, but the description never says when to use it versus get_flight_status or search_flights, and gives no prerequisites or exclusions.

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