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

Annotations already declare the mutation, destructive and idempotent profile, so the description's job is to add context — and it does: the change applies immediately to every site host and is independent of source drafts/publishing. It stops short of saying the previous favicon is overwritten (though destructiveHint covers this) and says nothing about the return value.

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?

Three tight sentences, front-loaded with the action and the clear-case, then the propagation scope, then the read path. No filler or restated title; slightly dense but every clause carries information.

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?

A two-parameter mutation tool with no output schema is well covered: action, null-clear semantics, scope of effect, and how to inspect the current value. Naming websiteAssets_list as the source of assetId would close the remaining gap for an agent that doesn't know where ids come from.

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 0%, so the description must compensate. It fully specifies the non-obvious semantics of assetId (string id from the asset library, or null to clear), leaving only websiteId undocumented — a self-evident parameter.

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 ('Sets the website's current favicon') plus the accepted source and formats (PNG, SVG, ICO from the website asset library). It is clearly distinguishable from sibling asset tools like websiteAssets_update or websiteSourceCode_files_upsert.

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?

Explains the clear-case (assetId: null) and points to where to read the current value (faviconUrl on GET /websites and GET /websites/find). It does not explicitly say to use websiteAssets_list to obtain an assetId, which is the obvious prerequisite for the non-null path.

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