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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered structurally. The description adds value beyond that by enumerating the returned fields and noting the dynamic 'whether it is still payable' state, though 'Creates nothing and moves no funds' largely restates the readOnlyHint.

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?

Two tightly packed sentences: the first front-loads the action and the full return payload, and the second delivers the safety constraint. No filler, no repetition of the title, and every clause carries information.

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?

There is no output schema, so the description must describe the return values itself — and it does, listing merchant, amount, payer cost, expiry, and payability. Combined with the annotation-covered safety profile and a fully documented single parameter, nothing needed to call it correctly is missing.

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% and the schema already specifies the exact accepted URL formats (payment-links/pl_... and payment-sessions/paymentSession_...). The description merely echoes 'a Coinbase payment link' without adding format, validation, or error-handling detail, so the baseline 3 applies.

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 ('Look up') and resource ('Coinbase payment link') and enumerates exactly what it returns: merchant, invoice amount, payer cost, expiry, and payability. The closing clause 'Creates nothing and moves no funds' implicitly separates it from the write-oriented sibling create_deposit_order, so an agent can distinguish it without opening the schema.

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 parenthetical '(e.g. an OpenRouter top-up)' gives a concrete usage context, which implies when the tool is appropriate. However, it never names an alternative (payment_status, create_deposit_order) or states when NOT to use it, so the routing guidance is only implied rather than explicit.

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