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

Beyond the readOnly/idempotent annotations, it discloses a real behavioral subtlety: absence of a hit reflects incomplete loading rather than nonexistence, which changes how an agent interprets results. It also states a prerequisite (a FactLot Registry must exist). It does not describe the response shape's ordering, size, or pagination, so a 4 rather than 5.

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?

Three compact sentences, each doing work: inventory contents, the call-before-missing guidance, and the prerequisite. The opening sentence is a long pre-verbal noun stack that delays the point slightly; a leading verb would front-load better.

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 return-value burden and does so by enumerating the listed categories and their metadata (sources, as-of dates), plus counts. Combined with the prerequisite and the interpretation caveat, an agent has everything needed to call and read the result.

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 there is no parameter meaning to convey and the baseline is 4. Nothing in the description misleads about inputs, though it spends no words confirming the no-argument nature.

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 enumerates exactly what the tool reports: counties with parcel/building counts, entity registries, crosswalk systems, plus sources and as-of dates. It is scoped to a specific registry file, which separates it from data-fetching siblings like registry_get or id_parcel. It never states the action verb explicitly ('reports/lists'), reading as a noun phrase, so it stops short of a 5.

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?

It gives an explicit trigger: call this before concluding a parcel or entity does not exist, with the reasoning that a miss outside these regions means not loaded, not absent. That is clear when-to-use guidance. It does not name a specific sibling or say when *not* to bother calling it, which keeps it below 5.

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