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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint. The description adds valuable context beyond annotations: free, no API key, watermark, does not touch quota, and returns the image inline. This enriches the behavioral profile without contradicting annotations.

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 sentences, each earning its place: action, cost/watermark, usage and alternatives. Front-loaded with the primary purpose, no filler or redundancy.

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 preview tool with a nested fields object and rich schema, the description covers the core purpose, cost, watermark, and alternative routes. It clearly states the return is an image shown inline, and the schema covers layout restacking. Minor gap: no mention of error scenarios, but that's not essential for basic invocation.

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%, with rich per-field descriptions (e.g., enum values, character limits, template-specific behavior). The description adds no extra parameter context beyond the schema, so baseline 3 is appropriate.

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?

The description states a specific verb and resource: 'Render a preset with the user's text and return the image'. It also distinguishes itself from siblings like render_card by mentioning the watermark and free nature, making the purpose unambiguous.

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?

Explicitly states when to use: 'Use it to show the user what their card will look like before they commit.' Provides clear alternatives for clean images (save_template + render_card on a paid plan) and explicitly contrasts with the editor's clean download. No ambiguity about when to choose this tool.

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