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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is largely covered. The description adds real value on top: renders are cached, nothing is stored about the requester, and free-tier/rate limits are mentioned, which an agent needs for retry and quota planning.

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?

Front-loaded with the output artifact and dimensions, then supporting details in compact clauses. Slightly dense with multiple parenthetical asides, but every sentence carries information relevant to calling the tool correctly.

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 13 parameters, an output schema present, and rich annotations, the definition is complete: it covers output format, caching, limits, and the template set without needing to explain return values, which the output schema handles.

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%, including enum values for template and theme and truncation limits for text fields, so the schema does the heavy lifting. The description only restates the template list and include_image, adding nothing beyond the structured fields – the baseline 3 is correct.

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 and resource: renders a 1200x630 PNG Open Graph/social-card image from a template and returns its public URL, size and meta tags. It also names the five templates and the include_image option, so the agent knows exactly what the tool produces without opening the 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?

States the intended use case (og:image and twitter:image tags) and ties its behavior to the sibling HTTP endpoint GET /api/og, noting shared engine, cache and free-tier limits. There is no explicit when-not or alternative tool to route to (none exists), but context is clear.

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