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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description goes well beyond them by disclosing the LLM-run cost per call, the 6-item cap, the project binding, the absence of reference images on created sheets, and explicit fail-open semantics (empty `created` list plus `note` rather than an error). These are exactly the behavioral traits an agent needs to budget and handle the call.

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?

Front-loaded with the core purpose and the sibling comparison, and every sentence carries distinct information (cost, cap, prerequisite, image gap, fail-open). It is dense and slightly long for a single-parameter tool, but there is 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?

With no output schema, the description still covers the return contract (a `created` list, plus a `note` on failure), the prerequisite workflow, and the cost model. Nothing an agent needs to invoke this correctly is missing.

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% and the sole parameter is fully documented there, so the baseline is 3. The description only implies the project scoping ('a project's material', 'binds each to the project') without adding format or sourcing detail beyond what the schema already states.

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 ('Create character sheets for the people found in a project's material') and immediately differentiates itself from siblings by naming lab_cast_gaps as its read-only counterpart and lab_create_character's territory. An agent can distinguish it from the other cast tools 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 explicit when-to-use ('Run lab_cast_gaps first if you want to see what it would create'), a hard operational boundary ('at most 6 per call'), and a downstream prerequisite chain (sheets need lab_generate_character_reference before lab_generate accepts them as `character_refs`). Nothing about sequencing is left to inference.

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