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

No annotations are supplied, so the description carries the full behavioral burden. It does disclose two genuinely useful facts an agent could not get from structured fields: the jurisdiction boundary and the billing cost of one credit. It says nothing about the return shape (single figure vs. banded breakdown), rounding, or what happens with non-numeric price strings, which matters for a calculator with 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?

A single front-loaded sentence covering jurisdiction, tax, and the covered regimes, with the cost note bracketed at the end so it does not interrupt the core statement. No filler and nothing repeated from the schema.

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 three-parameter calculation tool with full schema coverage, the essentials are present, and the credit cost is a nice addition. However, with no output schema the description should say what comes back (a tax figure, a banded breakdown, effective rate), and it leaves the currency and input-format expectations unstated — gaps an agent would hit on first call.

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, but the description adds real meaning by mapping its four named categories onto the parameter space — 'non-residential' clarifies how the boolean 'residential' flag interacts with 'buyerType', a relationship the schema lists without explaining. It still does not address the price parameter's dual number/string typing or expected units.

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 the specific tax (SDLT), the resource and scope ('a property purchase in England or Northern Ireland'), and enumerates the four rate regimes it covers, which distinguishes it from generic siblings like calculate or price_paid. What it never states explicitly is that it *computes* the liability rather than merely describing the rules, so the verb is inferred from context rather than written.

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?

Jurisdictional scoping ('England or Northern Ireland') implicitly excludes Scotland and Wales, which is a useful boundary, and the four buyer categories hint at which variant applies. There is no explicit guidance on when to prefer this over siblings such as calculate or house_price_index, and no statement of prerequisites (currency, whether fees/reliefs are included).

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