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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the safety profile is known. The description adds nothing beyond that: it doesn't say what happens on a duplicate key, whether registration is versioned/idempotent, or what a successful call returns. For a creation tool this is a notable gap.

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 tight sentences that front-load the action and then the key format. Every sentence is short, though the key-pattern and type enumeration duplicate the schema rather than earning their space.

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?

Given 7 parameters with nested objects but full 100% schema coverage, and no output schema expected to be explained, the description is adequate: it covers the primary identifier format and the type vocabulary. Richer options (isPii, valueDomain) are fully handled by the schema.

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 all 7 parameters, including isPii, isRequired, and valueDomain. The description's key-pattern and type-list sentences merely restate schema content (pattern regex, enum values) rather than adding new meaning, so baseline 3 is appropriate.

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 ("Register a new input variable") and follows with concrete constraints. It's unambiguous against lexq_facts_update/delete/list by virtue of the creation framing, though it never explicitly names siblings to distinguish itself.

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?

No when-to-use guidance, no prerequisites, and no mention of the adjacent lexq_facts_update (for editing an existing fact) or lexq_facts_list. The format rules given are input-shape hints, not usage guidance.

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