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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description's added context is the tax year (2026) and the employee-share scope; the enumerated return fields duplicate the existing output schema rather than disclosing new behavior such as rate caps or wage-base assumptions.

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?

Purpose, year, and scope are front-loaded in the first sentence, and the cross-reference closes it out. The inline return-field list is somewhat redundant given a formal output schema, but the whole definition stays short and scannable.

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 a single required numeric input, full schema coverage, and a published output schema, the definition covers everything needed to invoke the tool: what it computes, for whom, for which year. The only omission is explicit routing against the closely related US payroll tax calculators.

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?

There is a single parameter with 100% schema description coverage ('Gross annual salary in USD'), so the schema already carries the semantics. The description adds no syntax, units, or edge-case detail beyond it, making the baseline 3 appropriate.

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 gives a specific verb and resource ('Calculate US FICA taxes'), decomposes the acronym into Social Security + Medicare, and pins the scope to the employee share for 2026. It is clearly distinguishable from neighbors like calculate_us_federal_tax and calculate_us_paycheck, though it never names those siblings explicitly.

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?

'Employee share' implies the scope of use, and the pointer to list_bundles/'finance-us' gives a discovery path, but there is no explicit when-to-use or when-not-to-use guidance versus calculate_us_paycheck or calculate_us_federal_tax. Usage is implied rather than stated.

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