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

With no annotations, the description carries the full burden. It usefully discloses that missing inputs fall back to documented defaults, which is behavioral context beyond the schema, but it does not state that this is a pure/read-only computation, how errors are handled, or whether results come from an external rate source.

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 short and front-loads the action and outputs. It contains a noticeable duplication ("calculator calculator") and the semicolon list is slightly awkward, but overall it is efficient.

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 there is no output schema, the description should clarify return values more than it does. It lists the output metrics but does not explain their format, units, or whether all are always returned; the parameter side is complete because the schema is fully annotated.

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 in the input schema. The description adds only the default-fallback behavior, which is helpful but largely redundant with the schema's default values, so the baseline of 3 is 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 states a specific action (run the calculator) and enumerates the outputs it produces: all-in interest rate, capital-and-interest payment, interest-only payment, and arrangement fee. This makes the tool's function clear, though it does not explicitly differentiate it from the sibling calculator_describe tool.

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: the agent can infer this is the tool to use when it wants the listed mortgage calculations. There is no explicit guidance on when to use it versus calculator_describe or other siblings, and no exclusions or prerequisites are stated.

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