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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds useful context beyond that: a bot-verification challenge may occur and the production browser fleet is used without bypassing authentication or access controls, which tells the agent to expect possible friction. It doesn't describe rate limits or failure modes, so not a 5.

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 sentences, front-loaded with the purpose and return payload, then the sibling routing. The bot-verification sentence is a slight tangent but still earns its place as operational context. No filler.

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 return values need not be re-explained, and the description covers purpose, routing, and a caveat about verification challenges. Complete enough for a single-parameter read tool, with only minor room to note what happens if the URL is not a valid contributor page.

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?

There is a single required parameter with 100% schema description coverage; the schema already documents 'url' as the canonical contributor URL, and the description's 'from canonical author url' merely restates it. 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 ('Fetch') and resource ('Ars Technica contributor profile'), then enumerates the returned fields (byline, biography, contact email, headshot, recent articles). It also names the sibling tools it is not, so an agent can distinguish it from arstechnica_article and arstechnica_news without opening any schema.

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?

Explicitly routes the agent: 'Use arstechnica_article for one story or arstechnica_news for the general feed,' giving clear alternatives and their purposes. It stops short of stating the positive condition ('use this when you need an author's bio or their article list'), so it is a strong 4 rather than a 5.

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