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

Beyond the readOnly/idempotent annotations, it discloses the data source (usage_daily vs usage_key_daily), that keyless/dashboard usage is excluded, that a project-scoped key only sees its own project's keys, the maximum window length, and the stale_seconds freshness field. It also states the required `read` scope, which is genuine authorization context the annotations do not carry.

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?

Content is front-loaded with the core purpose and every clause carries information, but the first sentence is a long multi-clause construction rather than a scannable structure. It is dense without being wasteful, though a tighter lead sentence would improve it.

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 read-only analytics tool with no output schema, the description covers provenance, grouping, scoping limits, window rules, and even the one notable response field (stale_seconds). An agent has everything needed to call it correctly, including the scope requirement.

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 100%, so baseline is 3, but the description adds meaning beyond the schema: the semantics of group_by=key (per-API-key counters with key_id/name/prefix/project_id), the keyless exclusion, and a worked example of the exclusive `to` bound. These clarifications exceed what the schema alone communicates.

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 gives a specific verb-and-resource with scope: retrieval of billing-grade usage over a date window, sourced from usage_daily and grouped by day/project/engine/feature/key. It clearly conveys what the tool is, but it never names or contrasts with the closest siblings spicrawl_usage_summary or spicrawl_usage_reconciliation, leaving the agent to infer the boundary.

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 concrete context for use ('Use it to answer "how many requests/credits did I use, and where"') and operational conditions such as the default 30-day window and the 400-day cap. However, it offers no explicit when-not guidance or named alternatives, so the agent can't tell from this text when usage_summary would be the better choice.

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