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

Goes well beyond the annotations (which only cover read-only/idempotent/openWorld) by disclosing rate limits (30 lookups per IP per hour anonymous, 10000 per key per day signed in), the error payload shape, and that it 'contacts no business.' That is exactly the operational context an agent needs before calling.

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?

Front-loaded with purpose and the 'start here' routing instruction, then format, then returns, then limits and edge cases — a sensible order. It runs long and packs many clauses into single sentences, but nearly every clause carries actionable information; the trailing example is mildly redundant with 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?

There is no output schema, yet the description documents the return object fields ({agent_card, business, trade, town}), the meaning of the /b/ vs /c/ card paths, and the not_found error shape. Nothing an agent needs to call it and consume the result is missing.

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% and the schema already has the E.164 pattern and an example, so the description's format restatement is partly redundant. It does add meaning by explaining the number must be 'as customers dial it' and that any other format is rejected, which clarifies the real-world source of the value.

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+resource: 'Look up a business by its phone number in the Odile Direct directory and get its Direct card.' It also positions itself relative to siblings (send_to_business needs the id from this card; call_business availability via voice_fallback), so an agent can tell what this tool is and is not.

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?

'Start here' explicitly establishes this as the entry point before send_to_business, and it names the downstream alternative for unlisted US/Canadian numbers via voice_fallback/call_business. It also states a negative case (not on Direct → not_found with claim_url and listings_url), leaving little to inference.

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