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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context the annotations cannot: total cost is computed with announced price rises included, and unlimited data is subject to fair use. It still doesn't say whether results are cached, how the tracked link behaves, or freshness of pricing.

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?

The result contents are front-loaded before the filtering guidance, and the fair-use caveat is last. It is dense but every clause carries information; no filler sentences.

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 fields (price, upfront, contract length, total, data, network, seller, tracked link), which is what an agent needs to decide relevance. Coverage of pricing freshness and result ordering semantics is the only notable gap.

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 enum meanings are documented in the schema itself, so the baseline is 3. The description's filtering sentence is largely a restatement of the parameters, though "total cost with announced price rises included" does add meaning to sort=total.

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 resource (SIM-only plans from UK retailers on Vouchernaut) and enumerates exactly what each result contains — monthly price, upfront cost, contract length, total cost, data, network, seller, tracked link. It is distinguishable from find_phone_deals by the SIM-only scope, though it never names that sibling explicitly.

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?

"Filter by data, budget, network and contract length" implies when the tool is useful, and the fair-use note warns about one limitation. There is no explicit when-to-use-vs-alternatives guidance or statement of what the tool is not for.

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