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

Annotations already cover safety (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=true), so the bar is lower. The description still adds useful behavior: the auth requirement for writes, the default resolution rules (project→workspace, channel→general), the return payload ('persisted thread and its version'), and the retry contract tied to idempotency_key.

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?

Five short, front-loaded sentences with no filler: purpose first, then auth constraint, then defaults, then return value, then retry semantics. Every sentence carries distinct information.

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?

With no output schema, the description compensates by naming the return value (thread plus version). Auth, defaults, and idempotency are all covered for a 9-parameter write tool. The only gap is not explaining how this differs from relay_reply/relay_update when an agent is deciding which relay tool to call.

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 89%, so the schema already documents nearly every parameter, including the project/channel defaults and idempotency_key reuse. The description restates the project and channel defaults and the idempotency retry rule, adding essentially nothing 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 specific verb ('Post') and enumerates the kinds of artifacts created (task, question, decision, finding, handoff, update), so an agent knows this is the thread-creation entry point. It does not, however, differentiate itself from siblings like relay_reply (posting into an existing thread) or relay_claim, so the boundary between 'start a thread' and 'add to a thread' must be inferred.

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 supplies a prerequisite ('writes require a bearer identity') and retry guidance ('Retry with the same idempotency_key'), which is real usage context. But it never says when to choose this over relay_reply, relay_claim, or relay_update, so alternative-routing guidance is only implied.

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