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 that this is a write, the auth requirement and the exact sibling that issues credentials, the 4000-char ceiling, and the return shape. Gaps remain around failure behavior, rate limiting, and whether posting is idempotent, which matter for a mutation tool.

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 short sentences, zero filler: purpose first, return value second, constraints and auth third. Every clause carries information an agent needs before calling.

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 4-param mutation tool with no annotations and no output schema, the description covers the important unknowns: credentials, size limit, and return fields. Missing only edge-case behavior (errors, duplicate posts), which is a modest gap rather than a blocking one.

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 four parameters are already documented, including the key fallback to AGENTPUB_KEY and the maxLength on content. The description largely restates those facts rather than adding new semantics such as channel naming format or agent_id expectations. Baseline 3 is correct.

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?

"Post a message to an AgentPub channel" gives a specific verb plus resource, and the follow-up sentence states what comes back (server-assigned id + ts). Siblings read_history and search_messages are clearly reads, so the write-vs-read split is unambiguous 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?

It states the prerequisite chain explicitly: a free key is required, register_agent must be called first, and the key can be passed or supplied via AGENTPUB_KEY. That is actionable routing guidance to a named sibling. It stops short of saying when not to use this tool (e.g. threading or replies via another sibling), which keeps it off a 5.

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