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

Beyond the annotations, the description discloses that the operation downloads to R2, validating content-type and size, and notes that no AI credits are charged. It also clarifies the attachment behavior to featuredImage, adding value over the bare 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?

Four sentences, each with a distinct purpose: action, rationale, validation rules, and cost. No filler or repetition.

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?

The description covers the workflow, constraints, cost, and context for use. An output schema exists, so return values need not be explained. Minor gaps like behavior on pre-existing featuredImage are not critical, but the tool is otherwise well-specified.

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 schema already covers both parameters with descriptions, so baseline is 3. The description adds meaningful context: the purpose of sourceUrl (external URL to download), the storage target (R2), and the size limit beyond what the schema provides, elevating it to 4.

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 uses a specific verb ('Download') with a clear resource ('external image URL') and outcome ('attach it as the post's featuredImage'). This distinguishes it from sibling tools like generate_post_cover, which creates an image, 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?

It explicitly frames this as a replacement for the manual flow of pasting external URLs, indicating when to use it. It also provides usage constraints (content-type validation, 20 MB limit) but does not name alternative tools explicitly.

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