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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, covering the safety profile. The description adds valuable behavioral context about proxy fallback and normalization—traits not visible in annotations. It doesn't detail rate limits or output structure, but with the annotations covering safety, this is a strong contribution.

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 carry the entire message: purpose + scope, robustness behavior, and sibling routing. Every clause earns its place, and the core verb-resource pair is front-loaded. No filler or duplication of schema content.

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?

For a simple read-only fetch tool with full schema coverage, strong annotations, and no output schema, the description is complete. It explains what the tool does, how it handles blocking, and when to reach for a sibling—there are no critical gaps an agent would need to call correctly.

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 100%, so the schema fully documents all three parameters. The description adds no extra parameter-level meaning beyond contextualizing the URL as a feed. This meets the baseline for high coverage, though it doesn't elevate the semantics further.

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 states a specific verb ('Fetch and normalize') with a clear resource ('any RSS / Atom / RDF feed by URL'). It also differentiates from siblings by noting 'Use list_feeds first for curated sources,' which separates it from list/search tools. The word 'any' signals open-world coverage, aligning with openWorldHint.

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 tells the agent when to use this tool ('by URL' for arbitrary feeds) and names a concrete alternative condition ('Use list_feeds first for curated sources'). The CF-robust note also implies when it is preferred (direct fetch with proxy fallback), providing clear routing guidance without ambiguity.

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