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

Annotations only cover read-only/open-world, so the description carries the behavioral load and does so well: it discloses the illustrative-default fallback, that omitting rates can skew results several-fold, and that the response reports assumed values in `assumedInputs` with instructions to surface them. This is exactly the accuracy caveat an agent needs.

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?

Front-loaded with the core purpose and method logic before the IMPORTANT caveat, and every sentence is load-bearing. Slightly dense in the opening clause, but nothing is redundant.

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 8 parameters, 3 required, and no output schema, the description covers the critical unknowns: which inputs are commonly missing, what happens then, and that `assumedInputs` appears in the response. It stops short of describing the rest of the return shape, but the accuracy-relevant part is complete.

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 already 88%, so the baseline is 3, but the description adds meaning beyond the schema by framing the three optional rate inputs as lender-specific values most users will not have, and explaining the fallback when they are omitted. It doesn't add format/syntax detail beyond that.

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?

States a specific verb and resource (estimate the penalty to break a Canadian mortgage) and immediately scopes the calculation methods (three months' interest vs IRD, big-bank posted-rate method). This cleanly separates it from the other real-estate calculators such as mortgage_payment or mortgage_affordability.

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?

Gives clear context for use (breaking a fixed vs variable Canadian mortgage) and explains the branching rule. It does not name an alternative sibling or state when not to use it, but for a self-contained calculator the when-to-use guidance is clear.

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