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

Annotations declare readOnlyHint=false and destructiveHint=false, so the write/non-safe profile is already known; the description adds real context beyond that: a per-design token cost, the template-preference behavior ("Templates that hold every photo you supplied are preferred, so pass all of them"), and the photos-vs-images routing rule. It does not cover failure modes or what happens if no template matches, which keeps it short of a 5.

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 and the workflow are front-loaded in the first sentence, and each subsequent sentence carries usable information (alternative routing, photo preference, image-source split, token cost). It is a dense single paragraph rather than a structured list, which slightly hurts skimmability but not substance.

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 6-parameter, one-required, output-schema-backed tool, the description covers purpose, alternatives, cost, and the trickiest routing decision (two mutually exclusive photo sources). Return values are deferred to the output schema appropriately; the only omission is what the tool does when no suitable template is found.

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 the baseline is 3, but the prose adds meaning on top of the schema: it clarifies the photos-vs-images split ("Photos attached in the conversation go in `photos`; photos already on the web go in `images`") and reinforces the requirement to pass all photos for better template matching. It adds routing logic rather than restating types.

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 compound verb+resource: searches templates, renders each with supplied photos and copy, and returns several finished designs. It explicitly positions itself against siblings, saying it is "search and render together, so there is no need to call search_templates and fill_template yourself," so an agent can distinguish it 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 selection condition ("Use this when someone wants options") and names the two alternatives it replaces (search_templates, fill_template). It also adds a budget guideline — "Each returned design spends one agentic token" — which lets an agent decide how many designs to request.

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