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

Annotations already declare readOnly, idempotent, and non-destructive. The description adds meaningful context beyond annotations: requires an API key, revenue is returned in cents with a formatted convenience field, and zero views is a real answer not an error. No contradiction.

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?

Three sentences, each carrying distinct valuable information: purpose/metrics, usage boundaries, and operational details (auth, units, edge case). No filler or redundancy.

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 simple single-parameter tool with no output schema, the description fully covers what the agent needs: scope, metrics, return format, units, auth, and error semantics. It is complete enough to invoke correctly without additional documentation.

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 sole parameter 'days' is already fully documented in the schema (trailing window, range, default, examples). The description reinforces the trailing-window concept but adds no new semantic detail beyond the schema, so baseline 3 is appropriate.

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 uses a specific verb ('Summarise') with a clear resource ('the account's performance') and lists exact metrics (page views, revenue, subscriber count). It distinguishes itself from sibling tools by making clear this is the only whole-account analytics tool, not per-article.

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?

Explicitly states when to use ('how did I do this month' questions), and provides clear exclusions: cannot break down per article, covers trailing window ending today rather than arbitrary date range. This guides the agent away from inappropriate use.

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