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

The description discloses important behavioral details (downloads URL, stores it, null removes, 400 on invalid URL), but it directly contradicts the annotation destructiveHint=false because passing null removes the existing photo, which is a destructive operation. This is an annotation contradiction.

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 concise and front-loaded with the core action, but it repeats the tool title 'Update Customer Photo' at the start. The additional sentences on return values and error handling earn their place.

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 two-parameter tool with a rich schema and output schema, the description covers setting, clearing, return payloads, and error conditions. Nothing essential is missing for an agent to invoke it 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?

Schema description coverage is 100%, so the baseline is 3. The description largely restates the url parameter semantics already present in the schema, adding only the return behavior on set vs. clear, which is not parameter-specific.

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 names a specific action ('Download a public image URL and store it as the customer photo') and explicitly covers the null removal case, making the tool's purpose unambiguous and distinct from sibling update tools like updateCustomerNotes or updateCustomerTags.

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?

The description clearly states when to use the tool: to set a customer photo from a public URL or clear it with null. It does not explicitly name alternatives or exclusions, but the context is clear enough for an agent to select it over sibling tools.

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