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

Annotations already cover safety semantics (destructive, idempotent, open-world), but the description adds real value: the 400 failure condition when a URL cannot be fetched or is not a valid image, and the difference between the set and cleared responses. This is meaningful beyond the annotation set.

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 core action and tightly written, but the first line simply repeats the tool title, which is redundant given the title field. The remaining three sentences each 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?

An output schema exists, so explaining the returned image is not strictly required, but it is harmless. Combined with the error-condition disclosure, the definition gives an agent everything needed to invoke this two-parameter mutation 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%, and the schema already documents both id and url, including the null-removes behavior. The description largely restates that. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

States a specific verb and resource (update the customer photo) with the mechanism (download a public image URL) and the inverse operation (pass null to remove). An agent can distinguish it from updateCustomer, updateCustomerNotes, and updateCustomerTags at a glance.

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?

Clearly explains the two modes of use: provide a URL to set the photo, pass null to clear it. It does not name sibling alternatives (e.g., use updateCustomer for general fields), so routing guidance stops just short of the top mark.

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