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

No annotations are supplied, so the description carries the full disclosure burden and largely fails it. It doesn't say whether payments are assumed at end of period (ordinary annuity) versus beginning (annuity due), whether rate is a decimal or percent, or what the returned value looks like – and there is no output schema to fill that gap.

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?

It is short and front-loaded, with the function stated first. However, the trailing "🆓 5 free trial calls per signed wallet" sentence is promotional metadata that consumes the only remaining space instead of clarifying mathematical convention.

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 formula tool with zero annotation coverage, zero parameter documentation, and no output schema, the description should at minimum pin down rate units, payment timing, and the return value. None of those are present, leaving the agent to guess at conventions that materially change the computed answer.

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% and the description adds nothing about the three parameters. With names like "rate", "payment", and "periods", the agent still cannot tell whether rate is expressed as a percentage or a fraction, whether payment is per-period currency, or what units periods uses – the exact ambiguity that breaks a financial calculation.

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?

"Future value of an annuity" names a specific financial resource, but it essentially restates the tool name and title rather than clarifying scope. It never distinguishes itself from nearby siblings such as x402-annuity-pv (present value) or x402-future-value, so the agent has to infer which variant to pick.

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?

There is no when-to-use guidance at all – no statement of the scenario the tool fits, no prerequisites, and no pointer to the sibling annuity/PV tools. The only extra sentence is a pricing note (5 free trial calls per signed wallet), which is not usage guidance.

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