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

Since no annotations are supplied, the description has the full transparency burden. It does disclose the computed result categories and the fallback-to-defaults behavior, which is useful. However, it does not state whether the operation is purely read-only/stateless, how results are returned, or any assumptions/constraints beyond the documented defaults.

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 sentence with the key action and output list front-loaded, and no filler. The typo 'calculator calculator' and the compact semicolon-separated output list keep it from being a perfect 5, but it is still appropriately concise.

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 an eight-parameter calculator with no output schema and no annotations, the description could do more: it lists the output categories and notes default fallback, but it omits output shape/units, whether results are returned as a single object, and how this relates to the sibling enquiry/calculator-describe tools. It is adequate but not rich.

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 eight parameters are already described in the input schema (100% coverage), so the baseline of 3 applies. The description adds no per-parameter semantics beyond pointing to 'documented defaults,' but the schema carries that weight.

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 identifies a specific action ('Run') and resource ('Pub mortgage calculator') and enumerates the four outputs, so an agent can tell this tool computes mortgage figures. It does not explicitly contrast it with the sibling calculator_describe, and the doubled 'calculator calculator' wording is a minor blemish, so it falls just short of a 5.

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 implied: call this tool when the requested outputs are mortgage payment/interest/fee figures, and omitted inputs will use defaults. There is no explicit when-not-to-use guidance or mention of alternatives such as calculator_describe or submit_enquiry, so the guidance is adequate but not explicit.

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