contact_sheet

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

With no annotations, the description still discloses two key behavioral traits: a hard cap of 16 photos and the fact that output is a single composite image rather than individual files. It omits permission/read-only framing and what happens when a set exceeds 16 (paging is only implied by the schema's offset).

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?

Two sentences, zero waste. The output shape is front-loaded before the usage hint, which is the right order for an agent that needs to know what it gets back.

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 three-optional-parameter tool with no annotations and no output schema, the description covers the return artifact, the legend mechanism, and the size cap. The only gap is how a >16 set behaves relative to offset, which is left to the schema.

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 lane, files, and offset are already fully documented in structured data. The description adds only the implicit 16-item ceiling that motivates offset paging, which is marginal value. Baseline 3 applies.

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 (return) plus a precise output artifact: a numbered grid image with a legend mapping numbers to files. An agent can immediately distinguish this from preview_image (single image) or assess_photos without opening either 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?

"Use it to compare a set: composition, faces, closed eyes, missed focus" gives clear contextual guidance on when this tool fits. It does not name alternatives (preview_image, assess_photos, describe_file), so the agent must infer exclusions on its own.

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