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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the bar is lower. The description adds genuinely new context beyond that: the auth split between public keyless access and private OAuth access, plus a preview of the aggregated return content.

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 tight sentences with no waste. The core capability and valid range values are front-loaded, and the auth caveat is placed last where it belongs.

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?

Output schema exists, so return values need no explanation, and annotations cover the safety profile. Still, for a 6-parameter tool at 17% schema coverage, four parameters (user_id, project, timeout, writes_only) have no meaning documented anywhere, which an agent needs in order to call it correctly.

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 coverage is only 17% and there are no enums declared, so the description's enumeration of valid range values ("last_7_days", "last_30_days", etc.) is a real addition beyond the schema. But it leaves user_id, project, timeout, and writes_only entirely unexplained, so it only partially compensates for the coverage gap.

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 concrete verb and resource ("Fetch aggregated WakaTime coding stats for a user") and specifies the return shape (totals plus rankings by language, project, editor, OS), which implicitly separates it from siblings like summaries, durations, and commits. It does not explicitly name a sibling to avoid, so it stops short of 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?

It clarifies authentication context (keyless for public profiles, OAuth token via _apiKey for private ones), which is useful invocation guidance. However, it never says when to choose this over siblings such as summaries or leaders, nor does it state any exclusions, so usage is only implied.

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