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

Annotations already carry readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description reinforces this with 'Never creates an order' and adds that prices are live and in the chosen coin — useful behavioral context beyond the annotations, but it doesn't describe pagination or return mechanics.

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, zero filler — the primary purpose and scope are front-loaded, followed by the key routing and safety clarifications. Every clause earns its place.

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?

An output schema exists, so return values need no prose explanation, and annotations cover the safety profile. The description provides purpose, exclusions, and downstream compatibility. Minor gap: no mention of result volume or pagination, but given the output schema, the definition is essentially complete for correct invocation.

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 67% (coin and brand_slug described, country_code left bare). The description adds downstream meaning by tying the coin selection to output labels consumable by get_price/validate_order, complementing the schema. It doesn't compensate for the undocumented country_code, but the schema carries most of the load, so a baseline 3 is appropriate.

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 (list), resource (a brand's products/denominations), and adds scope (live, priced in chosen coin). Explicitly distinguishes itself from list_esim_plans and positions its output as the exact labels for get_price/validate_order, so an agent can select it correctly.

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?

Names the alternative tool list_esim_plans with the exact condition that triggers it (eSIM use), and clarifies it never creates an order, ruling out create_order. This is solid routing guidance, though it doesn't enumerate conditions for other siblings like get_price — but the core discrimination is covered.

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