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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds non-obvious behavior beyond them: the participant-based authorization rule (questioners/admins excluded) and a prompt-injection warning that message content is untrusted user text. It does not describe ordering or response shape, so not 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?

Four short sentences, front-loaded with the access-scope constraint, then pagination, then the trust caveat. No filler, and each sentence (including the untrusted-content warning) 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 read-only listing tool with no output schema, the description covers who can read, the default page size, how to page in both directions, and the trust level of returned text. It omits anything about ordering or the response envelope, but nothing required to invoke it correctly is missing.

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 0% for four parameters, so the description must carry the load. It clarifies before/after directionality (older vs new) and the default of 50, but leaves the meaning of 'id' implicit and never says whether before/after are message IDs or timestamps, nor what 'limit' maps to versus the 100 maximum in the schema.

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+resource (read private messages for tasks) and pins down the access scope: only tasks where the authenticated account is requester or executor, explicitly excluding questioners and administrators. That scope makes it distinguishable from write-side siblings like send_task_message without needing the schema.

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 concrete pagination guidance ('use before to read older pages or after for new messages') and states the default window of the latest 50, which tells an agent when to reach for those params. It stops short of naming an alternative tool or an exclusion condition, so it is clear context rather than explicit when/when-not routing.

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