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

Annotations already declare the safety profile (readOnly=false, idempotent=false, destructive=false, openWorld=false), so the bar is lowered. The description adds genuinely non-obvious behavior: exceeding the per-account source cap returns 403 limit_reached, which an agent needs to anticipate and handle. It stops short of covering duplicate-name behavior or auth requirements.

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?

Two short sentences with zero filler. The core purpose leads and the error condition follows, both front-loaded and easy to scan.

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 simple two-parameter creation tool with no output schema, the description covers purpose and one error case, and the schema covers inputs. It omits what is returned on success and how duplicate names or missing required fields are handled, leaving a modest gap.

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 both parameters (name, referer) are already fully documented with examples and stripping behavior. The description adds nothing about parameter meaning or format, so the baseline 3 is appropriate when the schema does all the work.

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 ('Create a traffic source'), which is unambiguous against siblings like create_label, create_proxy, and create_site. However, it does not differentiate itself from the sibling set beyond the noun, and the second sentence is error detail rather than scope clarification.

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?

There is no guidance on when to use this versus alternatives such as update_traffic_source or get_traffic_source, and no prerequisites or context about when a new source is warranted. The only conditional given is the failure mode when the account cap is hit, which is a constraint rather than usage direction.

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