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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real value on top: it discloses that results include currently running offers and a per-offer last-checked date, signalling freshness and that results are time-sensitive. It stops short of saying what happens when a shop isn't covered by any scheme, which is the main remaining behavioral gap.

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?

A single sentence, front-loaded with the answer shape (which schemes), followed by the extra payload (offers and last-checked date). Nothing redundant or padded.

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?

For a one-parameter, read-only lookup with no output schema, the description is nearly sufficient: it explains what comes back and that results are date-stamped. Only the empty/no-coverage outcome and result ordering are unaddressed, which is a minor gap given the closed-world annotation.

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 gives the shop/brand examples, so the description adds little beyond repeating 'named shop or brand'. Baseline 3 is right when the schema does the heavy lifting.

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 and scope: which UK loyalty schemes earn points at a named shop, plus the live offers and last-checked date. It carves out a distinct role from compare_loyalty_points_value and get_loyalty_scheme implicitly (per-shop lookup vs. valuation vs. scheme detail), but never names them, 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?

The framing ('Which UK loyalty schemes CardPoints covers') implies you call it when you have a shop and want to know what earns there, but there are no explicit when-to-use or when-not rules and no routing to the sibling tools. Usage is inferable, not stated.

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