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

The description goes well beyond the annotations by detailing specific behavioural traits: conventional PMI cancels at 80% and 78% LTV, FHA has a 1.75% upfront premium and MIP that may end after 11 years, VA funding fee is tiered by down payment and prior use, and waivers exist. This gives the agent a thorough understanding of the tool's scope and internal logic, and it aligns with the read-only and idempotent hints.

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?

The description is well-structured and front-loaded: a leading summary ('Mortgage insurance for any US loan programme, including the upfront charges most calculators omit') followed by four succinct programme-specific clauses. Every sentence conveys unique, necessary information without redundancy.

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?

Given the tool's complexity (9 parameters, 4 loan types) and the absence of an output schema, the description comprehensively covers the key calculations and caveats for each programme. It also notes that it includes upfront charges typically omitted, giving the agent a complete picture of 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?

With 100% schema description coverage, the baseline is 3. The description adds program-specific context that enriches parameter understanding, such as 'VA: the funding fee, tiered by down payment and prior use, and waivers,' which directly maps to downPaymentPercent, vaSubsequentUse, and vaExemptFromFundingFee. This extra context elevates the score above baseline.

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 clearly specifies that the tool calculates mortgage insurance for any US loan programme and enumerates the exact charges for each type: conventional PMI with cancellation points, FHA upfront MIP, VA funding fee, and USDA fees. This not only states the purpose with a specific verb and resource but also distinguishes it from sibling calculators like calculate_mortgage or calculate_amortization by focusing exclusively on insurance costs.

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 description provides clear context for when to use the tool: whenever mortgage insurance or related upfront fees for conventional, FHA, VA, or USDA loans need to be calculated. However, it does not explicitly state exclusions or direct users to alternative tools for non-insurance calculations, so it stops short of a perfect score.

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