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

With no annotations, the description carries the full behavioral burden, and it does disclose meaningful traits: scope depends on API key presence, and history depth is tier-gated (free 7 days, Pro 30). It omits that this is a read-only operation, the return shape, and any pagination behavior, so gaps remain.

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 terse sentences, purpose front-loaded, with zero filler. The aphoristic style ('With a key: everything on that key') is compact but slightly telegraphic, leaving some phrasing to be parsed.

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 two-parameter read report with no output schema and no annotations, the description covers the essentials: what is broken down, the auth-dependent scope, and the tier-based window. Missing details are modest — default value for days and confirmation of read-only, non-mutating behavior.

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 50% — run_id has no schema description — and the description compensates by explaining that run_id selects a single run and only applies without an API key. The tier limit restated for days ('Free shows 7 days, Pro 30') adds meaning beyond the schema's '1-30 (free max 7)'.

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 first sentence names a concrete report and its breakdown dimensions (per run, per tool, per model, per day), which is far more specific than a tautology. However, it never distinguishes this report from the sibling tools log_costs, usage_and_upgrade, or weekly_report, leaving overlap unresolved.

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 conditional invocation rules — pass run_id when unauthenticated, otherwise the whole key is covered — which is useful context. But there is no when-to-use guidance relative to the sibling cost/report tools, so an agent must infer which report to pick.

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