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

Annotations only declare readOnlyHint, and the description confirms 'Read-only' consistently while adding meaningful behavior detail: the distinction between 'sent_from_gmail' (actually delivered) and 'opened_in_gmail' (user may or may not have pressed send), plus note states for failed, timed-out, and still-waiting items. Auth requirements and limits are not covered, keeping it below 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?

Purpose and scope are front-loaded in the first clause, followed by the event enumeration and then the trigger examples. It is one long sentence, but each clause carries distinct semantic content (event types, send semantics, failure states), so density is justified rather than padded.

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, the description carries the burden of telling the agent what comes back, and it does so by enumerating the record categories (briefs, sent notes with send-mode, failures, waiting items, user responses). It does not describe return structure or ordering, which is a minor residual gap for a reporting tool.

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 the single 'days' parameter is already documented with default 7 and max 31. The description only restates the default, adding no format or boundary information beyond the schema, so the baseline 3 applies.

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 states a specific verb and resource ('what Your day did for the user over the last days days') and then enumerates the exact event categories covered: briefs written, notes sent, failures, pending, and user responses. This lets an agent distinguish it from siblings like my_day or send_daily_briefing without opening a 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?

It gives explicit trigger utterances ('what did Your day send?', 'did anything go out for me?', 'what did I approve this week?') that map directly to intent, which is strong when-to-use guidance. It lacks any when-not-to-use or explicit sibling exclusion, so it stops 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.