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

Annotations already declare readOnlyHint, idempotentHint and closed-world behaviour, so safety is covered. The description usefully adds a concrete worked example that reveals the expected output magnitude, but it does not disclose the proration convention (days-in-month vs 30-day basis) or rounding rule, which is the main behavioural uncertainty for this tool.

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?

Three short sentences with no filler; the illustrative example lands immediately. It is slightly less front-loaded than ideal, since the purpose sentence follows the example, and the trailing web-page URL adds little for an agent.

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 four parameters, two enums and no output schema, the description does enough to convey the core calculation but leaves the mode parameter and the underlying day-count/rounding method unexplained. An agent can call it correctly by relying on schema defaults, but cannot fully predict the returned figure's basis from the description alone.

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 the baseline is 3. The description restates 'rent' and 'move date' but never explains the mode parameter's in/out distinction, whose schema description ('Calculate for') is unhelpfully terse, nor currency handling.

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 names a specific verb+resource (prorated rent for a partial first month) and grounds it in a worked example ($1,500 rent moving in 11 March = $1,016.13). It is clearly distinguishable from sibling rent tools like rent_affordability_calculator and rent_vs_buy_calculator, though it never explicitly contrasts itself with them.

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 sentence 'Enter the rent and your move date to get the exact partial-month charge' implies the invocation path but states no when-to-use conditions, no prerequisites, and no alternatives. Usage is inferred rather than specified.

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