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

Annotations already declare this a read-only, closed-world operation, so the safety profile is covered. The description adds genuinely useful behavior: the calculation basis changes across eras (slab before 4 December 2014, slices after), relief windows for first-time buyers, additional-home surcharges stepping from 3% to 5%, and a non-resident surcharge from 1 April 2021. The final sentence also discloses that the return value is a GOV.UK page, which matters because there is no output schema.

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 jurisdiction and scope lead the definition, followed by the rate-era detail and the return-value note. The dense parenthetical packs several distinct rules efficiently, though the single sprawling sentence is harder to scan than a short bulleted breakdown would be.

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 four-parameter calculation tool with no output schema, the definition covers jurisdiction, valid date window, the legislative rate changes that drive the answer, and what the caller receives (a GOV.UK page). Only the numeric output shape and edge-case handling are unstated, and the GOV.UK URL disclosure largely compensates.

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 baseline is 3; every parameter is already documented in the input schema. The description does reinforce the temporal gating of nonResident (from 1 April 2021) and the meaning of the buyer categories via historical relief/surcharge dates, which is modest added context rather than new syntax or format detail.

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 verb and resource: computing Stamp Duty Land Tax for a purchase in England and Northern Ireland on a given completion date, evaluated against the rates in force that day. That historical, date-aware framing implicitly separates it from a current-rates sibling such as uk_stamp_duty_england_ni, but no sibling is named, so the differentiation is left to inference.

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 jurisdictional and temporal boundaries (England and Northern Ireland only; 1 December 2003 to today) function as real when-to-use and when-not-to-use context, since a Scottish, Welsh, or pre-2003 query clearly falls outside. No explicit alternative routing or exclusion sentence is provided, so it falls 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.