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

Annotations declare readOnlyHint=true, which aligns with description. Description adds critical behavioral context: date-sensitivity, handling of historical rates, US returns 0 for national VAT, and requirement to always pass invoice date for GB. No contradictions.

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 sentences, no redundancy. Front-loaded with key directive. Every sentence adds value. Perfectly compact for the information conveyed.

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?

Tool is moderately complex (multi-country, date-sensitive). Description covers main use cases and constraints adequately. Lacks mention of error handling for invalid inputs but given simplicity of return value (rate or 0), it's sufficient.

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 covers all 3 parameters (100% coverage), so baseline is 3. Description adds value by explaining parameter interplay: country determines tax type, state needed for US, date critical for GB. Clarifies default for country is GB.

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?

Description clearly states the tool returns VAT for GB and sales tax for US based on date/state. Distinguishes from sibling tools (none tax-related) with specific verb+resource. No ambiguity.

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?

Explicitly instructs to use before tax calculation, warns against recalling from memory, specifies when to pass invoice date and state code. Clear when-not-to-use: US without state returns 0. No alternative tools to differentiate.

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