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

With no annotations, the description carries the full burden and does so well: it discloses the return shape (ok, photo/needed/usable dimensions, message) and, crucially, that ok=false is a normal negative result rather than an error — a genuinely non-obvious behavioral trait. It stops short of explicitly stating the tool is pure/side-effect-free and cheap to call repeatedly.

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?

A single dense sentence that front-loads the verb and then layers purpose, scope, return contract, and failure semantics in order of importance. No filler, nothing repeated from the schema.

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 adequately documents the return payload and the failure convention, which is the main thing an agent needs to interpret results. The remaining gap is the undocumented layout parameters, which the schema names but never explains.

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 0% across 8 parameters, so the description must compensate. It only clarifies one relationship — that the photo size comes from the preset, or from custom millimetres when the preset is custom — and says nothing about cols, rows, gapMm, marginMm, or which paper enum values mean what.

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: "Compute the layout of an ID-photo print sheet", and the qualifier "without rendering it" implicitly separates it from render_photo_sheet_html. It does not name either sibling explicitly, so the differentiation is inferable rather than stated.

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 phrase "without rendering it" hints at the plan-vs-render split, but there is no explicit when-to-use/when-not guidance and no mention of list_photo_presets as the source of valid preset values. Usage is implied rather than routed.

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