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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, and the description adds operational context the annotations cannot carry: free, no authentication required, and rate limited. The rate-limit statement is unquantified, which keeps this short of 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?

Three short sentences, front-loaded with what it computes, then constraints, then access terms. No padding, though "Rate limited" is a bare assertion that could be trimmed or made specific.

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 only two simple scalar parameters and an output schema already defining the return shape, the description covers everything an agent needs: what is computed, the mode, the exclusions, and the access/rate constraints.

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% across two parameters, so the description must compensate. "Inclusive or exclusive" does explain the includeVat flag's intent, but the amount parameter's bounds and expected units (AED magnitude, non-negative) are never addressed in prose.

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 and resource ("Estimate standard 5% UAE VAT in AED") plus the key mode (inclusive or exclusive), which is concrete and actionable. It implicitly separates itself from uae_real_estate_vat by emphasizing the standard 5% rate, but never names the sibling, 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?

"Does not classify exempt or zero-rated supplies" gives one useful exclusion, which is more than most calculators offer. However, it never routes the agent to an alternative (e.g. uae_real_estate_vat for property scenarios), so the when-to-use guidance is only half present.

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