Top-up link

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

Annotations only say this is not read-only and not destructive; the description adds the crucial facts that no charge occurs, that a human must complete payment, that the URL is time-limited, and that the agent must not follow the link. That is exactly the behavioral context the annotations cannot convey.

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?

Three tight clauses: what it is, what it does in each mode, and the safety prohibition. The most consequential constraint (nothing is charged; a human must pay) is front-loaded with zero filler.

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 two-optional-parameter tool with no output schema, the description adequately covers both outcomes (URL vs tier list) and the human-in-the-loop requirement. Minor gaps remain: how long the link is valid and what the tier listing contains are unspecified, though neither blocks 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 100% and both parameters are already documented with defaults and examples, so the structured data does the heavy lifting. The description reinforces the meaning of create:true by describing the resulting behavior, but adds no new detail about tier_id or accepted values.

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?

"Card top-up for this account" names the verb and resource, and the description then splits the tool's two modes explicitly: with create:true it returns a checkout URL, otherwise it lists credit tiers. An agent can tell this apart from balance/usage/purchases siblings purely from the text.

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 conditional for the two operating modes (create:true for a checkout link, default for tier listing) and an explicit agent-behavior rule: never open or pay the link yourself. It does not name a sibling alternative (e.g. carpe_balance) for checking credit before topping up, but the when-to-use context is unambiguous.

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