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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered by structured data. The description adds real behavioral context beyond that — it explicitly declines to make eligibility determinations and gives a redirection target, plus the schema note that identity numbers and approval requests are refused. What it does not describe is the shape of the answer returned (for example, whether it is prose, cited figures, or a fixed template).

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 sentences, no filler. The positive use case and the scope list come first, followed by the exclusion and redirect, so the agent reads the selection rule before the caveat.

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 simple one-optional-parameter, read-only explainer with no output schema, the description supplies what matters: what topics are in scope and what decisions are out of scope, including the redirect. The only gap is that it does not say what the answer looks like when the question parameter is left empty versus supplied, beyond the schema hint.

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% and the single 'question' parameter already carries a detailed description covering its optionality, the empty-value behavior, and the PII prohibition. The description adds nothing about the parameter, so the baseline 3 applies; it neither compensates nor needs to.

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 ('explaining') tied to a named program (NSW Home Energy Saver) and enumerates the covered scope: loan cap, published income thresholds, funding use, and delivery. That scope list distinguishes it by content from generic siblings such as explain_loan_basics and explain_loan_options, though it never names a sibling explicitly to route the agent.

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?

Both directions are stated: use it when explaining the program's parameters, and do not use it to decide eligibility or approval. It even supplies the escalation path ('Send them to energy.nsw.gov.au'), which removes any guesswork about what to do with an eligibility question.

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