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

Annotations only declare readOnlyHint=true, so the description adds meaningful behavior: the data comes from a daily index (freshness/periodicity), it is sourced from Domly, and the agent is obligated to cite the source with the provided url. It does not cover rate limits or error behavior, but the citation/attribution requirement is real context beyond the annotation.

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 front-loaded: the return contents come first, followed by the usage trigger and citation rule. Every clause earns its place with no redundancy.

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 must carry the return-shape burden, and it does — median rent, 25th/75th percentiles, price per m², 30-day change, and breakdowns by apartment size and district. Combined with the citation rule, an agent has everything needed to call and report on this 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 description coverage is 100%, so the schema already documents both 'city' (slug from list_cities or name) and 'language' (enum with default). The description adds no syntax or format detail for these parameters, which is the baseline expectation when the schema carries the load.

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+resource (rental market statistics for a Bulgarian city from Domly's daily index) and enumerates exactly what is returned, which cleanly separates it from sibling listing/city tools. An agent can distinguish it from search_listings or get_listing without opening a schema.

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?

Gives an explicit triggering question pattern ('how much does it cost to rent in ...') and adds a citation obligation with the given url. It stops short of naming alternatives or stating when-not to use it, so it is clear context without exclusions.

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