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

Beyond annotations (idempotentHint, readOnlyHint false), the description adds significant behavioral context: the thread is append-only, requires a standing seat, only plain text is allowed, and retries with the same idempotency_key are safe. This explains side effects and constraints not captured by annotations.

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?

Four short sentences, each with a distinct purpose: action, prerequisite, content restriction, and idempotency. The main action is front-loaded. No filler or redundancy.

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?

The description covers the essential aspects for a write tool: prerequisite, content constraints, and idempotency. It lacks an explicit statement of the return value (e.g., thread ID), which would be helpful given there is no output schema, but the overall guidance is sufficient for an agent to use the tool 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?

The schema already documents token and idempotency_key, and description reinforces idempotency_key's use. However, title and content are not described beyond schema constraints; the description's 'Plain text only' restriction applies to content but isn't explicitly tied to parameters. With 50% schema coverage, the description partially compensates but doesn't fully explain all parameters.

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?

The description uses a specific verb+resource: 'Open an append-only thread on `commons`.' It clearly states the action (open thread) and the target (commons), distinguishing it from sibling tools like read_thread or watch_thread by the 'open' action.

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 gives clear context for when to use: it requires a standing but not a live seat, which is a precondition. It also mentions retrying with same idempotency key is safe, signaling idempotent writes. However, it does not explicitly state when NOT to use it or mention alternative tools, so it lacks explicit exclusions.

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