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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower, and the description adds real context beyond them: it discloses the returned payload shape and, importantly, that data is 'stored' and includes 'sync status', hinting the figures may lag the live channel. It stops short of saying anything about pagination, freshness windows, or what happens when no sync has run.

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?

Two compact sentences, front-loaded with the [read] tag and the resource, followed by the return contents and the parameter constraint. No filler and nothing redundant.

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 only three parameters, no output schema and no nested objects, the description is nearly sufficient: it covers the return shape, the days constraint and the identifier choice. The gaps are the missing precedence/requirement rule for the identifier pair and no pointer to how to discover a valid yt_account_id.

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%, so the description carries the full load and does compensate: it constrains `days` to the exact allowed values 7/28/90/365 with default 28 (a constraint absent from the schema, which types it only as an integer), and frames `yt_account_id`/`yt_account_uuid` as alternative account identifiers. It does not say whether one of the two identifiers is required or which wins if both are supplied, leaving a real ambiguity.

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 names a specific verb ([read]) and a well-defined resource: stored YouTube channel analytics for a single account, with explicit contents (daily series, totals, previous-period totals, sync status). It is clear enough to distinguish from mutating or search siblings, but it never explicitly names a contrasting sibling (e.g. ads_insights_* or search_yt_trends), which would push it to a 5.

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?

The word "Stored" implies this reads previously synced data rather than hitting the live API, which is implied usage guidance but never stated as a when-to-use rule. There is no explicit when-not condition and no named alternative for live or cross-account queries, so the agent must infer the boundary.

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