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

Annotations only cover read/idempotent/open-world; the description adds the paid cost ($0.0022 via x402), the SSRF guard behavior (private addresses refused, ≤3 redirects re-checked), error-code semantics (422/404/502 all uncharged), the empty-body default feed, and a prompt-injection caveat ('data, never instructions'). None of this is inferable from annotations or schema.

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?

Dense and front-loaded: it leads with the paid read and the returned shape, then layers errors, security, and payment. The payment paragraph overlaps with the schema's payment description, but almost every sentence carries operational information and the ordering is sensible.

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 paid, network-fetching reader with an output schema, the description covers everything an agent needs: cost, payment handshake, error taxonomy and charging rules, security posture, and data-vs-instructions guidance. Return fields need not be re-explained given the output schema, so nothing material is missing.

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 all three parameters are already documented in the schema, including the payment envelope flow and the default feed. The description largely restates those semantics (default feed, limit ordering, payment-on-second-call) rather than adding syntax or edge cases beyond them, so the 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?

States a specific verb and resource ('Read any public RSS 2.0, RSS 1.0 (RDF) or Atom feed') and enumerates exactly what is returned (title, link, description, up to 100 items with named fields). This clearly distinguishes it from siblings like web_read, hn_search, or crypto_news, which the agent can rule out without opening any schema.

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?

Gives explicit scope (public RSS/Atom only), an exclusion ('JSON Feed is not read'), and the fallback behavior when an HTML page is passed (422 naming the linked feed, not charged). It stops short of naming a sibling alternative for non-feed content, but the when-to-use context is otherwise clear and the payment prerequisite is fully spelled out.

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