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

Goes well beyond the annotations: it discloses caching on the video row with same-URL reuse, the force escape hatch, and the cost model ('downloads the clip and runs ffmpeg, so the first call takes a few seconds'). The readOnlyHint=false/idempotentHint=true pair is consistent with the described render-and-cache behavior.

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-loads the purpose, then rationale, cache behavior, and latency in a logical order. It is slightly long due to rhetorical asides ('just a URL and a promise', the PSNR anecdote), but each sentence still carries usable information.

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 explains what comes back (a tiled image and/or its URL), the caching semantics, and the latency to expect. An agent has everything needed to call it and set expectations for the first vs. subsequent calls.

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 cols/rows/width/preview are already fully documented in the schema. The description adds only a framing detail ('N frames spread evenly') and restates force's re-render purpose, which the schema already covers, so the 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 ('Build a contact sheet for a generated clip') plus the exact composition rule ('N frames spread evenly over its runtime, tiled into ONE image'). This clearly separates it from siblings like lab_render_frames or lab_letzter_frame, which produce different frame artifacts.

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 strong when-to-use motivation ('MCP has no video content type, so without a sheet a clip is just a URL and a promise') and a second use case (spotting camera drift). It does not name the sibling tools an agent might otherwise pick, so routing is by inference rather than explicit exclusion.

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