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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely non-structured context—that the payload is a per-country breakdown of sale/rent counts, currency, and filter availability—which compensates for the absent output schema, though it says nothing about format, caching, or rate limits.

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 sentences, both earning their place: the first defines the returned content, the second sequences the call before dependent tools. The most action-relevant fact (what it returns and why call it first) is front-loaded with no filler.

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 parameterless, read-only discovery tool with no output schema, the description supplies exactly the missing pieces: the shape of the returned records and its role as the prerequisite step for market-code-dependent tools. Nothing needed to invoke it correctly is absent.

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?

The tool takes zero parameters, so the baseline of 4 applies. The description correctly implies a no-argument call ('Call this first'), leaving nothing about inputs ambiguous.

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 verb and resource ('list_markets' = the countries Every Room covers) and enumerates exactly what each entry contains: home counts for sale and rent, currency, and supported filters. No sibling tool overlaps this scope, so an agent can place it immediately.

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?

Explicitly instructs 'Call this first to get the two-letter market codes the other tools take,' which is a direct when-to-use rule and an implicit prerequisite for the rest of the sibling set. Given no alternative tool exists for this purpose, no exclusion clause is needed.

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