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

Annotations only declare readOnlyHint and openWorldHint=false; the description adds substantial behavior the annotations cannot convey: the tool is paid ($0.002 USDC on Base per call), an unpaid call returns PaymentRequired, and the recovery path is _meta['x402/payment']. This is exactly the kind of auth/cost context that lets an agent invoke correctly on the first try.

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?

Front-loaded with the core action and use case, followed by the payment note and an example. Efficient overall, though the example args duplicate the schema's own examples and add little.

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 small pure-computation tool with readOnlyHint=true and no output schema, the description covers purpose, cost, and failure handling. The one gap is the return value (presumably a resulting date), which the description never states and which no output schema supplies.

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 the baseline is 3. The schema descriptions are thin ('e.g. 20'), and the description's example args restate the same values without clarifying formats, valid preset names, or whether days is a string vs number beyond what the schema shows.

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+resource: 'Add N NZ working days to a date', plus a concrete use case (OIA 20 working-day deadline). It is clearly distinct from validation siblings, but it never contrasts itself with nz_working_days, which is the closest relative and could plausibly be confused with it.

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 OIA deadline example implies the intended context, and the payment note tells the agent what to do when a call fails (retry with _meta['x402/payment']). However, there is no explicit when-to-use guidance versus nz_working_days, and no statement of prerequisites such as whether a wallet/payment credential is needed up front.

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