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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real value beyond them: no credit consumption, the return shape (image plus a one-line text note), and the default encoding. It stops short of describing failure behavior for invalid or missing ids, so not quite 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?

Four short sentences, front-loaded with the capability and its fallback, then return format, cost, and the follow-up action. No filler and no restatement of the tool name.

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 and seven fully documented parameters, the description fills the remaining gaps an agent needs: cost (no credits), return payload, client-capability branching, and the instruction to surface projectUrl to the user. Nothing essential to correct invocation is missing.

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 the baseline is 3; the description nevertheless reinforces the meaningful constraints (max four components, PNG unless format requests WebP) and adds a usage instruction not encoded anywhere in the schema. It could have clarified scale/padding intent, which restates nothing beyond the schema text.

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 (render screens as one inline image), the object (project screens), and the limit (up to four, side by side). It explicitly distinguishes itself from the sibling show_project, so an agent can route correctly 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?

Gives an explicit when-to-use condition (clients that cannot show apps) and a when-not with the named alternative ("Where your client can, call show_project instead"). It also routes overflow cases: "Render more than 4 in separate calls."

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