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

The description discloses that the tool performs a write operation (saves the favicon) and returns a new URL, which is beyond what the annotations provide (readOnlyHint=false, destructiveHint=false). It also mentions cache-busting, a behavioral detail not evident from the schema or annotations. The description does not contradict the 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?

The description is a single, concise sentence that front-loads the primary action and outcome, then adds the prerequisite. Every word earns its place, and the structure is easy to parse quickly.

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?

Given the tool has no parameters and an output schema exists, the description is largely complete. It explains the action, the prerequisite, and the return value. The only minor gap is that it doesn't explicitly state what happens if the account has no website, but the prerequisite mention implies the failure condition. Overall, it is sufficient for an agent to invoke the tool 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?

The tool has zero parameters, so the schema provides no parameter semantics. The description compensates by explaining what the tool does and what it returns, making it clear that no input is needed beyond the account context. Since there are no parameters to document, the description adequately covers the semantic gap.

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 clearly states the action ('Re-derive the account's favicon from its website, cache-bust it, save it and return the new URL') and identifies the specific resource (account favicon). It also distinguishes itself from related operations by noting the prerequisite of a website on the account, which helps differentiate it from similar refresh tools like refresh_client_favicon.

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 provides clear context on when to use the tool: when the account has a website and the favicon needs to be re-derived. It also mentions the prerequisite (set website with update_company), which is useful guidance. However, it does not explicitly state when not to use it or name alternatives like refresh_client_favicon, so it falls slightly short of full usage guidance.

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