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

Beyond the readOnlyHint=true annotation, the description adds meaningful behavior: funds go straight into the trader's own wallet, Cubicle never holds the money, and it reports when card purchases are not yet enabled. These are real traits not captured by the annotations, and no annotation is contradicted by the non-mutating link-generation role.

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 purpose is roughly front-loaded, but the sentence mixes the tool's function with downstream workflow instructions and an awkward meta clause ('Answers plainly when card purchases are not switched on yet'). Trimmed, it would be tighter without losing content.

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 is the only source on return values, and it conveys this only implicitly ('A link'). It covers the funding route and non-custodial nature but leaves the actual response shape and any flow/error semantics under-specified.

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 100%, so both 'owner' and 'amount_usd' (with its 20-10,000 range and default) are fully documented in the schema. The description adds no parameter detail, which is the expected baseline when the schema does the heavy lifting.

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 conveys that it produces a link to buy USDG via MoonPay by card, bank transfer or Apple/Google Pay, but frames it as a noun phrase ('A link to...') rather than a clear verb+resource, leaving the agent to infer it returns a URL. It does not differentiate itself from siblings such as onboard or vault_prepare.

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 sequencing guidance ('Then call onboard again: the next step is funding the vault') and notes the card-unavailable case, which is useful implied usage. However, it never states when to prefer this tool over alternatives like vault_prepare, so routing guidance is incomplete.

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