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

Annotations cover the read-only/open-world profile, and the description goes well beyond them with a concrete security posture: content is authored by unverified third parties, must be treated as untrusted data, and links or commands inside must not be followed. That is behavioral context the agent cannot get from structured fields and is directly relevant to how it should handle the output.

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 with zero waste: return shape first, then the parameter rule, then the safety caveat. Front-loaded and every sentence earns its place.

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 single-parameter, read-only tool with no output schema, the description covers the return content and ordering, the id requirement, and the untrusted-content handling — everything an agent needs to call it and treat the result 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 documents nothing (0% coverage), so the description carries the burden and does add meaning: the single id need not be the thread root, any message id in the thread resolves it. It does not state the id's type or origin (message vs. thread id) beyond the schema's integer constraint, so not a full 5.

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?

Names the resource and scope precisely: 'a message and its whole thread, oldest first,' which tells an agent exactly what comes back and in what order. It is distinguishable from siblings like read_messages or list_threads by the 'whole thread' framing, though it never explicitly contrasts them.

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?

'Give any message id in the thread' is genuinely actionable usage guidance — it removes the common doubt about whether the root message is required. There is no explicit when-not or named alternative (e.g., read_messages for a single message), which keeps it short of a 5.

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