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

Annotations already declare write (readOnlyHint=false), idempotent, and non-destructive behavior, so the 'stable request_id for safe retries' sentence largely restates idempotentHint. The credential guidance (Bearer header vs key argument, don't export chats containing the key) is genuinely additive behavioral context, but it is duplicated verbatim in the schema's key description, so the marginal value is limited.

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?

Purpose is front-loaded in the first clause, and the three sentences are each doing a distinct job (what it does, retry safety, auth/secret handling). It is slightly padded by the duplicated key warning, but not redundant or bloated.

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 write tool with an existing idempotency annotation and no output schema, the description covers the essential operational facts: access scope, retry idempotency, and credential handling. It omits moderation/permission subtleties (locked threads, role requirements) and any rate-limit or failure behavior, leaving small but real gaps.

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 only 40% (request_id and key). The description repeats the request_id/idempotency idea already in the schema, and says nothing about body, thread_id, or community_id beyond the loose first sentence. The three undocumented parameters are obvious by name, but the description does not compensate for the coverage gap.

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 (reply) plus resource (private community thread) and scopes it to threads 'this account can access'. The 'private community' qualifier hints at differentiation from the plain 'reply' sibling, though it never names that sibling or explains the distinction outright.

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?

The access constraint ('a private community thread this account can access') gives an implied condition for use, and the retry guidance implies a failure/retry context. However, there is no explicit when-to-use versus the sibling 'reply' tool, and no prerequisites for posting are stated.

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