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

readOnlyHint=true already covers the safety profile, and the description still adds substantial behavioural context: KNOWN CORRECTIONS (documented false assumptions plus what is actually true) are returned first, every hit carries a source and usage_policy that bounds quotation, and an empty result means 'nothing matched — it never means the claim is true'. That last clause prevents a serious misreading of the tool's output.

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?

Five sentences, each carrying a distinct load: trigger, tool identity, timing precondition, sourcing obligation, and empty-result semantics. The trigger is front-loaded and no sentence is filler or restatement of the title.

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?

No output schema exists, so the description carries the burden of describing returns — and it does: hits with source, usage_policy and corrections first, plus the empty-result interpretation. Nothing an agent needs to invoke this correctly or read its output 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 parameter docs are already unusually rich (authority floor default 0.85, corrections coming on top of anzahl), so the baseline is 3. The description adds no syntax or format detail beyond what the schema states, though it does reinforce the citation/usage_policy expectation that shapes how results are used.

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 — 'Ask the FilmOS knowledge layer' — and scopes it precisely to 'film-craft question: what a term means, which rule or convention applies, how something is usually done in camera, editing, sound or production'. It resolves the boundary against the wider lab_* family by declaring what belongs here ('answer from here, not from memory') versus what does not ('a craft fact you did not measure yourself in this session').

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?

Opening clause gives the trigger ('Use when the person asks a film-craft question'), and it names the explicit alternative to avoid ('not from memory') plus a pre-condition ('Call this before asserting a craft fact you did not measure yourself in this session'). When-to-use, when-not-to-use and the substitute behaviour are all present.

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