contact_sheet

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

With no annotations the description carries the full burden, and it does disclose the return behavior ('Returns the image path and the sheet inline') plus the poster variant. It omits the write-to-disk/destructive nature (overwriting a file) and any permission assumptions, which matter for an unannotated tool that writes 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?

Three tight sentences with the core action front-loaded, followed by the return and poster details. No wasted filler, though the poster clause is slightly compressed against the main description.

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 an 11-parameter media tool with no output schema, the description covers the primary action, both modes, the poster variant, and the return format. Remaining parameter detail is fully handled by the 100%-covered schema, so an agent has enough to call it correctly.

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 coverage is 100%, so all 11 parameters including modes, count caps, and thresholds are already documented in the schema. The description reinforces mode and poster semantics but adds little beyond what the schema provides; baseline 3 applies when the schema does the heavy lifting.

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?

Specific verb+resource: 'Tile timestamped frames of a video into ONE image', with the even/scenes modes and poster alternative spelled out. The 'whole recording in a single look' framing clarifies intent, but it never names the nearest sibling (sample_frames) to draw the boundary.

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?

The 'evenly spaced, or at the scene changes' and 'poster: true writes a single representative frame instead' phrases imply when each mode is appropriate. However, there is no explicit when-to-use versus alternatives like sample_frames, zoom, or screenshot, leaving the selection to inference.

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