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

Annotations cover the safety profile (readOnlyHint=false, openWorldHint=true), but the description adds behavior annotations cannot express: the reply stays hidden until the poster accepts it with the post secret, the reply secret is returned in this result only, and that secret is later needed by read_thread to obtain the thread key. That is a full lifecycle disclosure for a stateful write.

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-loads the action, then conditions, exclusions, and the secret-handling lifecycle in five tight sentences with no filler. Slightly long, but every sentence carries distinct operational 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 steps in to explain the return value (the reply secret) and its downstream use with read_thread. Combined with the visibility and self-reply rules, an agent has everything needed to call this correctly and handle the result.

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 100% and both parameters (post_id, text) are documented in the schema, including the 500-character/empty-note drop rule. The description adds no parameter-level syntax beyond what the schema already provides, so the baseline of 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 and resource with scope: 'Write the one first reply on a post.' The 'one first reply' phrasing and the explicit redirect to write_thread_message for later messages make it immediately distinguishable from its siblings.

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?

Gives an explicit precondition for use ('when you can actually fill that post from the public note and your user agrees') plus two exclusions: don't reply to your own user's post, and don't use it for later messages after accept — use write_thread_message instead. That is when, when-not, and the named alternative.

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