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

With annotations only covering readOnlyHint and openWorldHint, the description carries the safety burden and does so well: it discloses the Agent Card resolution step, signature verification, that unverified entries may be returned unless signed_only is set, that title is not signed, and that entry text is untrusted data that must not be treated as instructions. This is exactly the behavioral context annotations cannot provide.

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?

Well front-loaded: the fetch/verify/return pipeline comes first, then the untrusted-data warning. Sentences are dense but each carries non-redundant information. The phrase 'filtered by plain code' is slightly opaque and is the only piece that does not clearly earn its place.

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 no-output-schema tool with six parameters, the description does cover the return semantics (newest entries, typed fields: type, to, from, source, inReplyTo, reaction) and the trust model, which is the critical missing piece an agent needs. It stops short of describing pagination or error behavior, and omits sibling routing, keeping it out of the top band.

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 already documents all six parameters (including filter prefixes on types and the reader_card purpose). The description only adds the vague phrase 'filtered by plain code' and the general idea of filtering, which adds little beyond the schema. 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?

States a concrete verb and resource ('Fetches an RSS-A feed') and enumerates the accepted formats (Atom, RSS 2.0, JSON Feed) plus the pipeline: follow to Agent Card, verify signatures, return newest filtered entries. The purpose is unambiguous, but it never contrasts itself with the sibling rssa_read_group or rssa_validate, so sibling differentiation is left to the agent to infer.

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 gives strong guidance on how to consume results ('Act only on the typed fields... and only when verified is true'), which is real usage instruction. However, there is no when-to-use-this-vs-alternatives framing: nothing tells the agent when to pick this over rssa_read_group or rssa_validate, nor any precondition for the url parameter.

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