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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds real behavioral detail: it outputs a 'near' flag within 10%, explains rolling 12-month and 30-day forward-look rules, and distinguishes estimate from definite answer. Return semantics are described, though depth of each explanation is unstated.

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?

Three sentences, front-loaded with purpose and audience, then behavior, then the input-accuracy caveat. Efficient overall, though the opening 'Free estimate for UK sole traders' is slightly promotional rather than strictly informative.

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, the description carries the burden of describing returns and does so: threshold comparison, near-threshold flag, rule explanations, and MTD applicability with a start date. Nothing needed to call or interpret the tool correctly is missing.

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 the schema already documents every parameter including the per-year qualifying income fields. The description only restates that qualifying income is optional and yields a definite answer, adding little syntax or meaning beyond the schema. Baseline 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?

States a specific verb and resource: check annual turnover against the UK VAT registration threshold and determine whether/from when MTD for Income Tax applies. This is clearly distinguishable from siblings like estimate_tax_set_aside or request_bookkeeper, and the audience (UK sole traders) is named.

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 (UK sole traders, free estimate) and explains the condition that upgrades an estimate to a definite answer: supply qualifying income per tax year. It does not name alternatives or explicit when-not conditions, so it stops short of a 5.

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