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

Annotations already cover the safety profile (readOnly=false, destructive=false, openWorld=true, idempotent=false), and the description adds real context on top: the 72-hour link lifetime, that an expired checkout is replaced by a new one, and that payment unlocks autonomous spending from the balance. It stops short of saying what happens if the tool is called twice, leaving the non-idempotency hint to carry that.

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?

A single dense sentence front-loads the action and amount range, then uses a colon to enumerate the three returned URLs — efficient given there is no output schema. The nested parentheticals make it slightly heavier than needed but no sentence is 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?

With no output schema, the description correctly spends its budget naming the three URL fields and their purposes. Only the agent_key semantics and the choice against sibling pay-link tools are left uncovered for a two-parameter mutation with open-world behavior.

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 0%, so the description carries the burden and only partly discharges it. It gives the amount's semantic range ($10 to $10,000, whole-dollar units) which maps usefully onto amount_cents, but never explains what agent_key identifies or that the top-up is credited to that key's balance.

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 and resource ("Create a card top-up for a whole-dollar balance") and even scopes the amount range. It does not name or contrast with the sibling bounty_pay_link, which is the most likely confusion point for an agent choosing between payment-link 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?

The description explains what the balance does downstream ("pays bounties and part calls on its own"), which implicitly tells the agent this is a pre-funding action, but it never states when to pick this over bounty_pay_link or other funding siblings, nor any prerequisites beyond the implied agent_key.

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