generate_thumbnail

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

With no annotations, the description carries the full burden and does an excellent job: it discloses the returned data (inline image plus metadata fields), the public CDN URL, the authentication requirement, and the account-plan constraints for `hd` models. This is far beyond typical descriptions.

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?

The description is well-structured with clear sections (purpose, usage, return, auth) and is not excessively long. It earns its length by covering both usage and behavioral details, though it could be slightly shorter by moving auth instructions elsewhere.

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?

Given the tool has no output schema, the description compensates by explicitly describing the return format and metadata. It also covers prerequisites, costs, and model selection, making it self-contained for an agent to use correctly.

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?

The input schema already covers all parameters with rich descriptions, so the baseline is 3. The description adds some operational context (e.g., using `imageUrl` rather than base64), but it does not substantially elaborate on parameter meaning beyond the schema.

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 opens with a specific verb ('Generate') and resource ('thumbnail / social share image'), and further clarifies by listing concrete platforms (YouTube, Instagram, etc.). This clearly distinguishes it from the auth-focused sibling tools `login` and `logout`.

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?

It explicitly states when to use the tool ('Use this when...') with a list of use cases, and it mentions the prerequisite of an API key and the `login` alternative for auth. However, it does not explicitly describe when not to use it or mention alternative thumbnail-generation tools.

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