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

Beyond the annotations (readOnly, idempotent, non-destructive, closed-world), the description discloses real behavioral substance: the verdict taxonomy ('lowest we've recorded, no change, cheaper before and when'), that it surfaces rival shops cheaper today, that it returns a 'tracked link to buy', and its methodology limit ('Never uses shops' own "was" prices or RRPs'). The untracked-shop case is explicitly called out, which annotations alone could not convey.

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?

Two dense sentences that front-load the purpose and then the return contents; nearly every clause carries information. It is slightly run-on — the input enumeration and the output enumeration are packed into the same sentence — but nothing is padding.

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 carries the full burden of describing returns, and it does: verdict categories, competitor pricing, and the buy link. It also covers the degraded case (untracked shop) and the data provenance, leaving no material gap for a single-parameter read tool.

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 there is a single parameter, so the baseline is 3. The description earns a point above baseline by documenting the `ref` format as "<store>/<product>", a syntactic detail the schema description ('or a ref') omits, plus the barcode digit range context.

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?

Names a specific verb and resource ('whether a product's price at a UK shop is a real deal') and pins the data source ('Vouchernaut's own record of that shop's prices'), which cleanly separates it from generic siblings like get_product or search_products. It also enumerates exactly what the answer contains (today's-price verdict, cheaper shops, buy link), so an agent knows the shape of the result before calling.

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 description makes clear what inputs to pass (product page link, barcode, name, or ref) and states a boundary condition — it 'says plainly when the shop isn't one whose prices are tracked' — so the agent knows the failure mode. It never names an alternative tool or says when to prefer price_drops / get_product instead, so it stops short of full routing guidance.

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