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

With readOnlyHint and destructiveHint already covering safety, the description adds real value: it explains that required facts absent at runtime throw and that the engine never defaults to 0, cites P-015 and ACT-032, and explicitly marks the data as static and cacheable in-session. It stops short of describing the response shape, which matters since there is no output schema.

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?

The purpose is front-loaded in the first sentence and each subsequent sentence contributes a distinct rule (conditional facts, no-default behavior, P-015, SET_FACT exemption, caching). It is dense with internal error codes and jargon, but no sentence is redundant.

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 zero-parameter, read-only metadata lookup with no output schema, the description supplies enough for correct use: what is returned conceptually, the meaning of factRequired, and the failure mode. The remaining gap is the literal structure of the returned data, which an agent must discover at call time.

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 schema carries no semantic load and the baseline of 4 applies. The description correctly does not invent parameter guidance, instead spending its words on output semantics such as the factRequired flag and conditional refVar behavior.

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 states a specific verb and resource ('Retrieve runtime fact requirements per Action type') and elaborates on the exact content returned: which input facts must be present per action, with MUTATE_FACT and SET_FACT as concrete examples. It does not name sibling tools such as lexq_facts_list or lexq_requirements to disambiguate, so it falls 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?

Usage is implied rather than stated: an agent infers it should call this to learn which facts a payload must carry. The only explicit guidance is 'Static data, safe to cache in-session', with no mention of when to prefer a sibling lookup or any preconditions for calling.

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