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

With annotations declaring readOnlyHint=false, idempotentHint=true, and destructiveHint=true, the description adds important context: it issues a prepaid card, requires ext_id for idempotency, and clarifies that IMBA does not create the booking. It also warns against using payment_source=stars and client_id. This goes beyond the structured annotations without contradicting them.

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?

The description is dense and purposeful, with the core purpose front-loaded and usage constraints packed into a few sentences. Minor redundancy ('prepaid from this agent') and mixing endpoint info with instructions slightly hurt clarity but overall it's efficient.

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 an 8-parameter tool with 25% schema coverage, the description explains the essential params and critical constraints. It doesn't detail every optional field, but the required usage context and idempotency semantics are covered. Some gaps remain around card product selection, but the reference to core.card_product.id helps.

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?

Input schema coverage is only 25%, so the description must clarify key parameters. It explicitly says ext_id is required and is an idempotency key, and that imba_product_id is core.card_product.id. It also warns against payment_source=stars (though payment_source isn't in the schema). This meaningfully compensates for the schema's gaps.

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 states a specific action ('Issue a Visa/MasterCard prepaid') and the resource (a virtual card), plus the concrete use case (paying merchants that require a card). It also names the endpoint and disambiguates from other card operations by mentioning what IMBA does not do.

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?

The description explains when to use this tool: when the agent needs to pay merchants requiring a card, and explicitly notes constraints like 'Never payment_source=stars' and 'Never pass client_id'. It doesn't explicitly name sibling alternatives, but the card-issuing context plus 'IMBA does not create the booking' gives useful routing context.

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