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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior. The description goes further by disclosing that figures are computed live upstream, that results include the tax year, currency, underlying assumptions and a source page, which tells the agent how much to trust and cite the output. It stops short of noting edge cases such as unsupported gross ranges or failure behavior.

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 dense but well-ordered sentences: purpose first, then inputs, then return shape. Every clause carries information, though the return-value enumeration is long enough that it verges on a wall of text for a single paragraph.

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 must describe return values and does so thoroughly (gross/net/deductions annual and monthly, typed breakdown, effectiveRate, tax year, currency, assumptions, source). Combined with full schema coverage and annotations covering safety, an agent has everything needed to call and interpret it.

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 coverage is 100%, so parameter meaning is largely carried by the schema and baseline is 3. The description adds country-to-parameter mapping but is slightly narrower than the schema (it lists only england|scotland and madrid|cataluna while the enum also includes wales and northern-ireland), so it does not meaningfully exceed the schema's own documentation.

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 ('net salary after income tax and social contributions') with an explicit scope (ten named countries) and provenance (LifeByNumbers calculators). An agent can distinguish it from rate-lookup siblings like uk_rates_lookup or get_fact 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?

Implicitly tells the agent this is the tool for take-home pay questions and clarifies which optional parameters apply per country (US state/filingStatus, CA province, UK region, ES region). However, it never says when to prefer this over siblings such as uk_rates_lookup, nor states exclusions or preconditions, so selection remains partly inferential.

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