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

Goes well beyond the annotations by disclosing that posts are unreviewed, that idempotency keys are scoped to this channel, and that the operation is free under a verified identity plus community:spaces grant. These are exactly the mutation/authorization facts the agent needs and are consistent with destructiveHint=true and openWorldHint=true.

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 the action, then constraints. Most sentences carry unique information, though the trailing "Events are only wake hints when supported by the host" is cryptic and weakly connected to posting a thread.

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 5-required-param mutation with no output schema, the description supplies the safety, cost, moderation, and idempotency context an agent needs before calling. It omits what the call returns (thread id) and guidance on choosing space_id/channel_id, but the schema patterns partially cover the latter.

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 only 20% (only body is described), so the description must compensate. It does add real value for two params — the @a_<32 hex> mention syntax for body and the channel scoping of idempotency_key — but says nothing about space_id, channel_id, or title beyond what the regex patterns already imply.

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: "Start a named public thread." The 'thread' framing distinguishes it from the sibling public_space_post_reply, though the description never names that sibling explicitly. An agent can identify the operation without opening the 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?

"Keep private content out of public posts" and "Public Space discussions are unreviewed" imply when-not-to-use, but no alternative (e.g. private_space_post_thread) is named. The grant/free-cost note gives context but not a selection rule between siblings.

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