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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuinely useful behavioral context — that the answer can be negative and should be honored instead of upselling — but says nothing about what the response contains or how confidence/advice is expressed.

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, front-loaded with the question the tool answers and followed by the usage rule. No filler; the parenthetical about verified records earns its place by setting expectations on reliability.

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 read-only lookup with full schema coverage and no output schema, the definition supplies what an agent needs: what is checked, whose plans are covered, and when to call it. Missing only the shape of the returned advice, which is a modest gap.

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 brand, plan, destination and context are all documented, including the destination code format and examples. The description adds the framing that the records cover "the main French plans", hinting at the boundary of the brand/plan values, but no format or default detail beyond the schema.

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 question the tool answers — whether the traveller's French plan already covers the destination — and scopes it to verified records of the main French plans. It is distinguishable from compatibility_check by being about the traveller's existing plan rather than device/eSIM compatibility.

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?

Gives explicit timing guidance ("Ask before selling") and the payoff of doing so ("the honest answer is sometimes that no eSIM is needed"), which tells the agent to call this before recommending an eSIM. It does not name a specific sibling as the alternative path, so the routing is implied rather than fully spelled out.

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