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

Annotations already declare read-only and idempotent, but the description goes further: exact validation rules, refusal of private/internal addresses and redirects, and an explicit statement that nothing is charged. An agent knows precisely what will and won't happen on invocation.

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: what it builds first, what it returns next, then the constraints. No filler, and the most decision-relevant facts (nine URLs, grid order, no charge) lead.

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 only two parameters and no output schema, the description covers the missing return-shape info (thumbnails, price, set_hash) and all validation behavior. Nothing an agent needs to invoke it correctly is absent.

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 baseline 3; the description adds real meaning by specifying grid ordering (left to right, top to bottom) and the per-image constraints (JPEG/PNG, 10 MB, plain https, no redirects, no private addresses) that the schema only gestures at. The email parameter isn't elaborated, which keeps it below a 5.

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 action (build a printable 3x3 set from nine URLs) with exact scope and returns, making it clearly distinct from place_order, get_pricing, and check_order.

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 'Nothing is charged and no order is created' line plus the set_hash handoff to place_order implicitly positions this as the pre-check step. It doesn't explicitly say 'call this before place_order instead of ordering directly,' so the routing guidance is strong but not fully spelled out.

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