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

Annotations already establish read-only, idempotent, closed-world semantics, so the bar is lower. The description adds a genuinely non-obvious trait beyond them: results are re-verified live when cached data is over an hour old, which tells the agent to expect a slower call and trustworthy freshness. It stops short of covering error/not-found behavior.

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 compact sentences with the freshness rule front-loaded and an inline example that earns its place given the undocumented schema. Only the sentence-fragment style slightly weakens readability.

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 two-parameter lookup with no output schema, the description should state the return shape and the behavior when merchant_id is omitted. It conveys the concepts of availability and price but not their structure or the single-merchant vs multi-merchant branching.

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 description coverage is 0%, so the description must compensate, and it does partially via a concrete example showing slug-style IDs ('prusa-mk4s', 'prusa3d'). It never explains that merchant_id is optional or what omitting it returns, so the required/optional asymmetry is left implicit.

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 the two returned values (availability and price) and the per-merchant scope, which is specific enough to distinguish it from get_product and compare. It does lean on the title for the verb ('check'), but the resource and scope are unambiguous.

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?

There is no statement of when to use this versus siblings like compare or get_product, nor any prerequisite or exclusion. Usage is only inferable from the name and the phrase 'per merchant'.

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