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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuine value by disclosing the shape of the result (band-by-band breakdown, effective rate, cross-buyer-type comparison, total cash needed with deposit), which is important since there is no output schema. It omits any note on rate-table currency/update caveats, but that is minor for a pure calculator.

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?

One dense sentence that front-loads the core purpose and then enumerates the outputs. It is long but every clause carries information (scope, outputs, buyer-type comparison); no filler or repetition.

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 usefully enumerates the returned figures, and the read-only annotations cover safety for this pure calculation. The main residual gap is the absence of any guidance on jurisdiction limits (e.g. Scotland/Wales not covered beyond the implicit England/NI note) or how the buyer-type comparison relates to the buyerType parameter.

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 schema already documents all three parameters and the buyerType enum. The description adds only marginal semantics, notably the 5% additional-property surcharge, which is not restated in the schema. Baseline 3 is appropriate when the schema does the heavy lifting.

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 (calculates) plus resource (Stamp Duty Land Tax) and scopes it geographically (England or Northern Ireland) and temporally (current rates). A reader can distinguish it from the sibling BTL/CGT/Section 24 calculators immediately.

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 content — you use it when buying a property and need SDLT figures — but the description neither states when to prefer it over siblings like analyse_buy_to_let_deal or calculate_btl_mortgage, nor any exclusions. It hints at coverage (first-time buyer/home mover/additional) without routing the agent.

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