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

Annotations already declare this is a read-only, non-destructive, closed-world operation, so the safety profile is clear. The description adds that it estimates based on days late, but does not disclose any further behavioral traits such as whether it's a point estimate, whether it uses current HMRC rates, or any limitations. Minimal added context beyond annotations.

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, well-structured sentence that front-loads the purpose and efficiently lists the three penalty types and the required inputs. No wasted words.

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 read-only estimation tool with full schema coverage and annotations, the description is adequate but not thorough. It lacks any mention of output structure, assumptions (e.g., current HMRC rates), or edge cases. An agent has enough to invoke it, but could benefit from more context about the estimate's nature.

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%, meaning every parameter is fully documented in the schema. The description only restates the high-level inputs and adds no syntax, format, or default information beyond what the schema already provides. Baseline 3 is appropriate when the schema does all the work.

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 (Estimate) and precisely enumerates the resource (Self Assessment late filing penalties, late payment penalties, and late payment interest on tax due). It clearly distinguishes itself from siblings like calculate_late_payment_interest by covering all three penalty types.

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 implies usage by stating the inputs (days late, tax paid), but provides no explicit when-to-use or when-not-to-use guidance. It does not mention the alternative calculate_late_payment_interest or when this broader estimate should be preferred. Usage context is only implied.

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