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

With no annotations at all, the description carries the full burden and does exceptionally well: it discloses card creation timing, hard amount cap, merchant lock, single-use behavior, issuer relationship, no retention of card numbers, registration side effect, and the budget-link fallback.

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 key purpose is front-loaded and the structure is logical (purpose → examples → behavior → trust → onboarding). It is longer than strictly necessary, with some redundancy like 'single-use' and 'cannot be spent twice', but every section adds relevant operational context.

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 no-annotation, no-output-schema tool with nested parameters, the description is complete about side effects, registration, budget handling, and trust boundaries. It does not describe the returned card payload, but the rest of the context is strong enough to make the tool callable.

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 already 75%, so the baseline is 3. The description adds meaningful context beyond the schema by tying 'payee' to the merchant lock and 'amount' to the hard cap, and by noting the reason is recorded but never used for the decision.

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 opening sentence names a specific verb ('Get'), a specific resource ('single-use virtual card'), and an immediate purpose ('buy something right now'). The following examples make the scope unmistakable and implicitly distinguish it from sibling approval/history/record tools.

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 gives a clear 'when to use' with an extensive list of procurement scenarios (SaaS, domains, hosting, checkout). It does not explicitly say when not to use it or name an alternative, so it stops short of a 5.

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