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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the description's job is lighter. It adds that the tool lists sources and the API version, and importantly states 'Keyless', which clarifies authentication requirements. No contradictions with 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?

Two concise sentences with no wasted words. Each sentence serves a purpose: the first states what the tool does, the second gives usage guidance and keyless info. Front-loaded with the core action.

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's simplicity (no input parameters, no output schema, low complexity), the description covers the essential: what is returned, how to use the output, and authentication. Could optionally mention if there is pagination or rate limits, but not necessary for this simple tool.

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, and the schema description coverage is 100% (empty). The description adds meaning beyond the schema by explaining what the output contains (sources and API version) and how it can be used. This fully compensates for lack of parameter details.

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 verb 'list' and the resource 'every news source' plus API version. It distinguishes from sibling tools like search_articles by explicitly mentioning using the names to filter that tool. The purpose is specific and unambiguous.

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 a clear usage scenario: use the names to filter search_articles. It also notes 'Keyless' indicating no authentication needed. However, it does not explicitly exclude other contexts or mention when not to use this tool, leaving some guidance implicit.

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