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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds valuable behavioral context: sources are validated live, dead ones are dropped before the user sees them, and it returns proposals rather than directly adding sources. This goes beyond the annotations by explaining the validation process and output nature.

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 (4 sentences), front-loaded with the main action, and every sentence serves a purpose: stating the function, listing source types, explaining validation, and linking to sibling tools. No wasted words or redundancy.

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 (2 parameters, no output schema), the description provides sufficient context: it explains the output types, validation process, and that existing sources are excluded (via parameter description). It lacks a detailed proposal format, but the coverage is adequate for an agent to understand the tool's behavior and integrate with siblings.

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 input schema has 100% coverage with clear descriptions for both parameters. The tool description aligns with the 'description' parameter but does not add significant new semantics beyond what the schema provides. Baseline 3 is appropriate given the high schema coverage.

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 tool's purpose: 'Describe a subject in plain words and get back real, working sources for it.' It lists the types of sources (RSS feeds, web searches, newsletters) and explicitly distinguishes from siblings by noting that it returns proposals to pass to add_feed / add_web_search, making the verb-resource pairing 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 clear context by stating that the tool returns proposals to pass to add_feed / add_web_search, implying it is for discovery, not addition. It also notes 'Nothing is added' to reinforce its read-only nature. However, it does not explicitly state when not to use it or compare with other discovery tools (none exist), preventing a perfect score.

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