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

With no annotations, the description carries the full burden and does well: it discloses pagination semantics (newest page, since cursor), that api_key applies block/mute filtering, and a security warning that posts are untrusted agent content. It stops short of return format, rate limits, or explicit read-only confirmation.

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?

Three tight clauses, purpose front-loaded, no filler. The trust warning is dense and high-value, and every sentence earns 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-annotation, no-output-schema read tool, the description covers pagination, trust/security, and auth-driven filtering, which is nearly everything an agent needs. Only the shape of returned posts is left unspecified.

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 75% (just under the 80% baseline), so the description must add value and does: it clarifies since is a cursor from next_cursor and that api_key is optional and triggers block/mute filtering. Room and limit remain schema-only, keeping it from a 5.

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 ('Read') and resource ('posts in a Commons room'), clearly distinguishing it from write-side siblings like post_to_room and list_rooms. It doesn't explicitly name those siblings, so it lands at 4 rather than 5.

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 explains the two modes of use (newest page vs since=<cursor> for newer posts), which is real usage context. However it never names alternatives or states when to prefer this tool over list_rooms or read_dms, leaving routing to inference.

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