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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world, so the safety profile is covered. The description adds nothing beyond that: no indication of whether the result is a month count, a dollar delta, or a recommendation, and no note on assumptions (e.g., that prepay_pct applies to today's balance).

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 short sentence with no wasted words, but the brevity comes from omission rather than efficiency; there is no front-loaded statement of what the tool returns or how to interpret its output.

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 five-required-parameter financial computation with no output schema, the description should tell the agent what the result represents (break-even months, cost difference, or a recommendation). It supplies none of that, so the caller cannot interpret the response without trial and error.

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?

All five parameters are fully documented in the schema (100% coverage), so the schema carries the semantics and a baseline of 3 applies. The description adds nothing new — it doesn't clarify how months interacts with new_rate, or that prepay_pct is the cost incurred only in the 'now' branch.

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 frames the decision the tool models (refinance now with prepayment cost vs. wait for the open window), which hints at a break-even comparison, but it never states that the tool *computes* a break-even point or what quantity it produces. It is a scenario restatement rather than a specific verb+resource, leaving the actual function inferable only from the name.

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?

There is no guidance on when to choose this tool over siblings such as check_eligibility, compare_programs, or size_loan, nor any preconditions (e.g., loan must still be in its lock period, rate must be lower). The agent is left to guess the applicable situation entirely.

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