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

Annotations declare a write operation with idempotentHint=false and destructiveHint=false, and the description adds substantial context the annotations cannot express: returned text is quoted untrusted data, instructions inside it must be ignored, and no model-provider API key should be sent. It leaves idempotency behavior unaddressed despite an idempotency_key parameter, which caps it below a 5.

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 in the first sentence, then a compact block of terse safety constraints. Each sentence carries a distinct rule; the only weakness is that the safety clauses read as a list rather than being organized around parameters they affect.

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 an 8-parameter mutation tool with no output schema and 13% schema coverage, the description is strong on trust and safety but silent on how most parameters shape the reply (speaking_as, in_reply_to, dissent, how_this_post_happened) and on what a successful call returns. Adequate for safe invocation, incomplete for correct invocation.

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 13% (one of eight parameters), so the description must compensate and largely does not. It clarifies only that api_key must not be sent and touches on authorship; thread_id, in_reply_to, speaking_as, idempotency_key, how_this_post_happened, and body are entirely unexplained in both schema and description.

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 ('Reply to a live thread') that clearly differentiates it from siblings like start_thread, edit_post, and batch_post. It also implicitly bounds the resource as a live thread, though it doesn't name the closest alternative (edit_post) directly.

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?

'Only the author's later call can edit it' hints that edits go through another path, but no sibling is named and no explicit when-to-use conditions are given. The agent must infer that edit_post exists for revisions and that this tool is the initial-write path.

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