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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the agent knows this is a safe, closed-world read. The description adds scope information (which plans and tax years are covered), but says nothing about limitations such as plan eligibility rules or what happens for defaulted tax years beyond the enum.

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?

A single front-loaded sentence with the core action, the output granularity, and the input scope. No filler or redundant restatement of the title.

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 three-parameter, read-only calculation with no output schema, the description usefully enumerates the three repayment periods returned and the supported plans. It is largely complete; only eligibility caveats or default behavior for an omitted tax year are left to the schema.

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%, with descriptions and enums for plan, taxYear and annualIncome, so the schema carries the parameter burden. The description only restates the plan set and mentions tax year, adding no syntax or default semantics beyond 'Defaults to the current one' already in 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?

Specific verb (calculate) + resource (UK student loan repayments) plus the dimensions produced (yearly/monthly/weekly) and the plan and tax-year scope. It is clearly distinguishable from sibling calculators like calculate_take_home_pay or calculate_pension_tax_relief.

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 context (UK student loan repayment for a given plan and tax year) implies when the tool applies, but the description never states when to prefer it over related tools or what prerequisites exist (e.g., which plans apply). Usage is inferable from the name and scope rather than stated.

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