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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuine behavioral context beyond that: it is a band-by-band computation at fixed 2026/27 rates, it discloses the relief thresholds (nil to £300,000, up to £500,000) and the surcharge mechanics (+5% on every band, 2% non-resident). It stops short of saying how the result is presented.

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 dense sentence with the jurisdiction and rate year front-loaded and zero filler. The parenthetical thresholds make it slightly crammed, but every clause carries substantive rate information that an agent would otherwise have to guess.

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?

There is no output schema, so the description carries the burden of indicating what comes back, and it does not: it never says whether the tool returns a total liability, a per-band breakdown, an effective rate, or relief amounts. For a three-parameter calculator this is a noticeable gap, though the input-side semantics are fully covered.

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 coverage is 100%, so the baseline is 3 and the schema already documents all three parameters. The description does add meaning for the buyerType enum by spelling out what first-time buyer relief and additional-property treatment actually mean in money terms, and it clarifies that nonResident is a 2% surcharge rather than an alternative classification. That is real but partial value on top of an already-complete schema.

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?

Names a specific tax (Stamp Duty Land Tax), a specific jurisdiction (England and Northern Ireland) and a specific rate year (2026/27), so the agent knows exactly what is being computed. The geographic scoping implicitly routes away from the sibling calculators scotland_lbtt and wales_ltt, though it never names them.

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 by the jurisdiction and rate-year framing rather than stated: an agent can infer this applies to English/NI residential purchases in 2026/27. There is no explicit when-to-use statement, no exclusion clause pointing at scotland_lbtt or wales_ltt, and no statement of prerequisites or limits.

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