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

The description discloses important behavioral traits beyond the annotations: the upload permanently overrides extracted metadata, the response's image_url is the new card image, and invalid formats are rejected before upload. This is especially valuable since annotations only indicate the tool is not read-only and not idempotent.

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?

Every sentence earns its place: purpose, the either/or input choice, validation constraint, permanence and response field, then a guidance note on crop. The most important information is front-loaded, and the description is compact without being vague.

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 mutation tool with no output schema, the description explains the key behavioral outcomes, input constraints, and optionality of crop. An agent has enough information to decide whether to use this tool and how to populate its parameters 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?

With 100% schema coverage, the description benefits from a baseline of 3. It adds meaningful context for source_url (server fetches a merchant product photo), image_base64 (creator-supplied bytes), and crop (optional, rarely needed, omit to show the whole image). This is helpful but not radically more than the schema already conveys.

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 and resource: 'Replace the image on a link's card'. It goes beyond a generic label by framing the tool as the fix for wrong metadata-extracted images, which clearly distinguishes it from related link or page image tools. The purpose is unambiguous and actionable.

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 gives a clear use-case signal: use this when metadata extraction grabbed a logo, favicon, or placeholder. It does not explicitly name alternative tools or state when not to use it, but the context is strong enough for an agent to route to this tool.

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