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

Annotations already show readOnlyHint=false, so mutation is expected. The description adds valuable behavioral context: the server can auto-discover feeds from site addresses, error messages are precise, and the tool is idempotent (per annotation). This goes beyond what annotations provide. No contradiction 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?

The description is concise (two sentences) and front-loads the main action. Every sentence adds value, no fluff. Could be slightly more structured but is well within good practice.

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 simple parameter schema (2 mandatory fields, no output schema), the description is complete enough. It covers the main purpose, the extra discovery feature, error behavior, and doesn't need to explain return values since there is no output schema to reference. Still, a note on what the tool returns (e.g., success confirmation) would be helpful but not essential.

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 coverage is 100% and the description adds no new detail for the parameters beyond what the schema already states (e.g., url can be a site address). The description does mention auto-discovery, which maps to the url parameter, but adds no extra semantics for source_id. Baseline 3 is appropriate.

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 it adds an RSS/Atom feed to a topic inbox, and even distinguishes it from similar tools like remove_feed. The added detail about accepting plain site addresses with automatic feed discovery adds significant clarity.

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 hints at when to use it (adding a feed to an inbox) and what happens on failure, but it does not explicitly say when not to use it or how it compares to add_web_search or other sibling tools. The usage guidance is implicit, not explicit.

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