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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds real behavioral value by naming the three outputs produced (limit, interest-only draw payment, repayment jump), which tells the agent what the computation yields even without an output schema.

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 tightly packed sentences front-load the formula and the outputs, with no filler; the trailing web-page URL is extra but harmless. Slightly over the minimum, but every clause earns its place.

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 stateless calculator with no output schema, the description covers the two things that matter: what goes in (via the formula) and what comes out (the three computed figures). Nothing essential is missing, though it never mentions assumptions such as variable-rate behavior or that results are estimates.

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 all seven parameters are already documented with units, defaults and ranges in the schema. The description reinforces the relationships among home, cltv and mortgage via the formula but adds no new parameter-level syntax or format detail, making the baseline 3 appropriate.

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 the resource (HELOC) and states the exact computation up front: home value × CLTV minus mortgage, plus the interest-only draw payment and the repayment-period jump. That is specific enough to distinguish it from generic siblings like loan_to_value_calculator or mortgage_calculator without opening the schema.

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?

Usage is only implied: an agent can infer you call this to estimate a HELOC limit and payments, but there is no explicit when-to-use, no prerequisites, and no routing against the many overlapping sibling mortgage/loan tools. Adequate but leaves the selection decision to inference.

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