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

Annotations already carry readOnly/idempotent/non-destructive, so the description's job is to add substance — and it does, disclosing the conditional discount-code policy (code shown only where the brand approves AI assistants, otherwise the saving plus the store page that reveals it) and that a tracked buy link is returned. It omits failure behaviour for an unknown ref, which is the remaining 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?

It is a single ~60-word run-on sentence with stacked parentheticals, which makes the conditional code-disclosure clause hard to parse. The core lookup is front-loaded, but the nested asides cost readability rather than saving space.

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, so the description correctly takes on the burden of enumerating return contents, including the price-history shape (lowest, typical, now). It does not cover what happens on a missing/invalid product, which is the one thing an agent still has to guess.

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's own description already gives the ref format and URL alternative, so the description adds only framing ("by its `ref` ... or its vouchernaut.com page"), not new syntax or constraints. Baseline 3 is appropriate.

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?

The description names a specific single-resource lookup and enumerates exactly what comes back: variant prices/stock, best discount code, post-code price, price history, delivery, cross-store comparison and a buy link. That distinguishes it from the sibling search_products (plural) without naming it explicitly, so it falls just short of a 5.

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?

Usage is only implied: the tool takes a `ref` or a page URL, so an agent infers it applies when it already has an identifier rather than a keyword query. No alternatives (search_products, check_deal, get_store_offers) are named and no when-not condition is stated.

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