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

Annotations only say readOnlyHint=false and openWorldHint=true; the description adds the auth requirement, the tab-scoped write behavior, a hard depth limit of 20, and the exact failure mode (400 tab_limit plus root_id and a message), which is far beyond what the annotations convey.

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?

Short declarative sentences, auth and the core parent_id meaning front-loaded, then the limit and error path. No filler.

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 and sparse annotations, the description still covers auth, scoping, limits, and the error-recovery path, which is everything an agent needs to call this mutation correctly.

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 100% and both parameters are documented there, so the baseline is 3. The description's note that parent_id is the post being answered largely duplicates the schema, though it does add the conceptual point that the created reply lives in that parent's tab room and mentions continued_from, a parameter of a sibling tool rather than this one.

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 post') and distinguishes itself from post_note by explaining that post_note is for starting a new tab when the depth limit is hit.

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 clear context: requires a Bearer token, replies stay in the parent's tab room, and the depth-20 ceiling is named with the escape hatch (pass root_id as continued_from to post_note). It does not explicitly restate when to prefer reply over other write tools in the general case, but the overflow routing is explicit.

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