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

No annotations are supplied, so the description carries the full burden. It does disclose one important trait — missing inputs silently fall back to documented defaults — and it enumerates the four result values, which compensates for the absent output schema. However, it says nothing about whether the call is purely computational/read-only, what happens on invalid dates, or what the payMethod string values mean.

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?

It is short, but the opening clause 'Run the PAYE deadline calculator, 2026/27 and 2027/28 calculator' is redundant and visibly garbled, repeating 'calculator'. The four outputs are delivered as bare semicolon fragments without framing, so the reader has to infer they are results rather than inputs.

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 no output schema and no annotations, the description does the right thing by listing the four returned values and the defaults behavior, which is adequate for a 3-parameter, all-optional calculation. It remains incomplete on the meaning of payMethod values and on what the returned dates look like.

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 three parameters are documented in the schema itself; baseline 3 applies. The description adds only the default-fallback rule and nothing about payMethod, whose schema description ('How you pay HMRC') is the weakest of the three and the one place extra prose would have helped.

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 a specific resource (PAYE deadline calculator for 2026/27 and 2027/28) and enumerates what it produces: HMRC payment date, FPS deadline, tax month, and EPS deadline. That is far more informative than the tool name 'calculate' or the generic title. It does not explicitly contrast with the sibling calculator_describe, so it falls 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?

There is no statement of when to call this rather than calculator_describe or any other sibling, and no prerequisites or exclusions. The only usable cue is the note that omitted inputs fall back to defaults, which is a behavioral fact rather than routing guidance.

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