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

Annotations only declare safety hints (readOnlyHint=false, idempotentHint=true, destructiveHint=false); the description goes well beyond by describing export-fidelity semantics (source shorter than clip duration ends early and subsequent material shifts forward), black-frame handling ('a clip that would render black says so (\'schwarz\')'), the per-frame answer contents, and cost ('Free (no credits)'). With no output schema, this disclosure of return content and quirks is exactly the added value the description should carry.

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?

Purpose is front-loaded and every sentence carries weight: the export-fidelity sentence is dense but necessary for interpreting results, and the exclusion clause routes to the right sibling. It is on the long side and slightly packed with jargon (src_in_s, 'schwarz'), which keeps it just short of a 5.

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 five-parameter tool with no output schema, the description covers return shape (per-frame clip position, clip_id, clip start and offset; black frames flagged), workflow placement, cost, and rendering caveats. Nothing an agent needs to call and interpret this tool correctly appears 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%, so all five parameters (seq_id, sekunden, preview, profile, kachel_breite) are already documented with defaults and bounds. The description adds interpretive context about what sekunden map to ('Each second is mapped like the export maps it') and the 12-frame limit, but no syntax or format detail beyond the schema. 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 precise verb and resource ('See the CUT at exact seconds of the finished film: up to 12 frames, tiled into one image and shown') and explicitly demarcates scope against siblings: 'NOT in the image: lens/grade, lower thirds, the AI badge — that needs lab_start_export.' An agent can separate it from lab_render_frames, lab_contact_sheet, or lab_letzter_frame without opening any 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 an explicit workflow position ('Use it after lab_timeline_apply to check cut points before exporting') and names the alternative for the excluded content ('that needs lab_start_export'). Both the when and the when-to-use-something-else are stated, not inferred.

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