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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description goes well beyond them: Messages-permission gating of preview lines, hard exclusion of content written by under-18s, threads returned as COUNTS only, and the "not open yet" state of the pro inbox. These are genuine behavioral constraints an agent could not infer from structured fields.

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 one-line pitch before the detail, which is good. However, it then enumerates the entire return surface (identity, week, threads, pending, badge) in a single dense run-on even though a full output schema already exists, so much of that clause stack is duplicative rather than additive.

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 no-parameter aggregator with an output schema, the description covers everything an agent needs: what is included, what is deliberately excluded (under-18 lines, pro inbox), the privacy precondition, and the follow-up cursor for `events`.

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?

Zero parameters, so there is nothing to document and the baseline is 4. The description correctly spends no effort on inputs.

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 aggregate resource (the person's whole day: identity, personas, week, open threads, pending answers, badge count) and explicitly positions itself as the entry point against the list_*/whats_waiting siblings. An agent can tell it apart from `events` because the description says it returns the `next` cursor for that tool.

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?

"Start every session here" is an explicit directive for when to call it, and the `next` cursor note tells the agent to poll `events` for later changes. It stops short of naming when NOT to use it or which sibling supersedes it for a specific slice (e.g., whats_waiting vs this).

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