list_sources

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

With no annotations, the description carries the full burden. It discloses the return metadata fields, notes that isContentAvailable requires subscription, and explains default vs non-default sources. This provides meaningful behavioral context beyond just 'list sources', though it omits minor details like pagination or authentication.

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 concise, front-loaded with the main purpose, and uses bullet points for clarity. Every sentence adds value, and it avoids redundancy with the schema or the tool name.

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 low complexity (no params, no output schema), the description fully covers what the tool returns (domain, isDefaultSource, isContentAvailable), how to use it, and its relationship to sibling tools. It is complete for its scope.

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 schema coverage is 100% (empty schema). The description adds semantic context about how to interpret default sources and their relationship to search_articles, which is valuable beyond the schema.

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 'Get a list of all available news sources' with a specific verb and resource. It also distinguishes itself from sibling tools by positioning as the discovery step before using search_articles, making its purpose 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?

It explicitly says 'Use this to discover available sources before filtering with the search_articles tool' and mentions the optInSources parameter, giving clear context on when and how to use it. It does not explicitly say when not to use it, but the guidance is sufficient for a discovery tool.

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