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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so the safety profile is covered. The description adds the APY/APR and any-compounding capability, which is useful behavioral context, but says nothing about return format, rounding, or what happens with edge rates.

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?

Effectively one front-loaded sentence that leads with the tool's function before the cross-product note. The trailing web-page URL is mildly promotional rather than operational, which keeps it short of a 5.

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 six parameters, three enums, no required inputs and no output schema, the description should at least say what comes back (interest earned, maturity value, APR/APY pair). 'Interest earned by maturity' hints at the result but the output shape is left unstated, so an agent knows how to call it but not fully what to expect.

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 all six parameters (rate, term, deposit, currency, rateType, compounding) are already documented in the schema. The description adds the APY/APR framing and compounding-agnostic scope, which lightly clarifies rateType and compounding, but nothing about defaults, ranges, or units beyond the schema.

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?

Names a specific verb+resource ('CD calculator for interest earned by maturity') and adds a distinctive capability (APY to APR conversion for any compounding). However, with siblings like fd_calculator, compound_interest_calculator, apr_calculator and simple_interest_calculator, it never states how it differs from them, so the agent cannot disambiguate on purpose alone.

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?

Usage is implied rather than stated: the note that it is 'the same maths for Canadian GICs, UK bonds and GCC deposits' tells the agent the tool generalizes across deposit products, which is mild routing guidance. There is no explicit when-to-use vs. when-to-prefer fd_calculator or compound_interest_calculator, and no prerequisites.

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