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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world). The description adds operationally useful context beyond them: free, no authentication required, and rate limited. The rate limit is not quantified, which keeps it from a 5.

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?

Four short sentences, fully front-loaded: purpose, tax rule, exclusions, then cost/auth/limits. No filler or repetition of schema content.

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?

An output schema exists, so return values need not be described. The description covers scope exclusions, the key tax rule, auth, and rate limits. Minor gap: it never states the actual VAT rate assumptions being applied (e.g., standard rate vs. zero/exempt outcomes) for a tool whose whole job is a rate-based estimate.

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 0%, so the description bears the param burden. It usefully explains the domain logic behind firstSupply and yearsSinceCompletion (zero-rating only on first supply within three years), but leaves amount, propertyType, and includeVat entirely to the schema. Partial compensation, so baseline 3.

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?

Clear verb (estimate) plus resource (VAT on ordinary UAE commercial/residential property) and currency (AED). It implicitly separates itself from the generic uae_vat sibling via "not transfer fees" and the property-type scope, but never names an actual alternative. Purpose is unambiguous even without explicit sibling routing.

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?

Provides concrete when-not guidance: no transfer fees, no mixed-use, no specialist properties, and the residential zero-rating condition (first supply within three years of completion). It stops short of naming a specific alternative tool to use instead, so it is clear context without explicit routing.

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