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

Annotations cover the safety profile (readOnly, idempotent, openWorld), and the description adds context they cannot: the full return shape, that summaries are HTML-stripped and capped at 500 chars, caching behavior via the `cached` field, and metering specifics (shared 100 calls/day per IP free bucket, 1 credit per call over x402, no API key). That is real operational context for a rate-limited external call.

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?

Front-loaded with purpose, then usage, then return shape, then metering - the order matches how an agent needs to consume it. Every sentence carries distinct information; even the metering line prevents a failed call loop.

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?

No output schema exists, but the description enumerates the return object's fields, documents the summary truncation, and discloses cost limits - which is everything an agent needs to call this correctly and interpret the result.

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% and both parameters (url with 2048-char cap, limit 1-20 default 10) are fully documented in the schema. The description adds nothing parameter-specific, so the baseline 3 applies.

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?

Opens with a specific verb+resource ('Read an RSS or Atom feed and return its latest items') and explicitly names the sibling tools web_fetch and web_map as the wrong choice for adjacent tasks. An agent can distinguish it from every other web_* tool without opening a 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 an explicit 'When to use' condition (user wants latest posts/news, or a feed URL is known and headlines+links are wanted) and an explicit 'Do not use' with the two correct alternatives for article text and URL discovery. Nothing is left to inference.

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