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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: a '[Premium]' tier gate that can affect whether the call succeeds, and an enumeration of the returned content (specs, price history, days on market, verdict, comparables), which matters since no output schema exists.

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 front-loaded sentence with the verb, lookup key, and payload contents in order of importance. Nothing is redundant with the schema, and the premium marker sits up front where it is noticed before invocation.

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 premium lookup with no output schema, the description covers what is returned and the tier constraint. It stops short of saying what happens when the premium entitlement is absent (error vs. partial payload), which is the main remaining 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?

With one parameter at 100% schema description coverage, the schema already explains the id format and provenance ('starts with L', from search_listings / get_price_drops'). The description adds only 'by id', so baseline 3 applies.

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 retrieval ('Full details for one listing by id') and enumerates the payload (specs, price history, days on market, fair-price verdict, comparables). This distinguishes it from list-oriented siblings like search_listings and get_price_drops, though it never names those siblings 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?

There is no explicit when-to-use or when-not guidance; usage is only implied by 'by id' and the schema note that the id comes from search_listings / get_price_drops. An agent can infer the search-then-fetch workflow but must supply the routing logic itself.

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