Read this period's spend

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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds genuinely useful context beyond annotations: the underlying endpoint (GET /api/usage), required scopes (usage:read, luca:read), 'data sensitivity: redacted', and that idempotency is not required.

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?

Front-loads the core purpose in the first sentence, then presents operation/scope metadata in compact lines. Slightly boilerplate-heavy (endpoint, scopes, idempotency) but each line carries machine-usable information rather than filler.

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?

An output schema exists so return values need not be explained, and annotations cover the safety profile. The description adds auth scopes, redaction level, and workspace-override behavior; the only real omission is any explanation of the `since` window parameter.

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 67%; workspaceId and workspaceSlug are documented in the schema and the description clarifies they override the environment-configured default. However, the `query.since` parameter has no description in either the schema or the description, leaving the time-window control only vaguely implied by 'for the period'.

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?

States a specific verb (Read) and resource (model spend) with scope details: 'for the period, rolled up by agent and by day, against the plan's cap.' This is clearly distinguishable from the sibling luca_usage_messages, though the description never explicitly names or contrasts with it.

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?

Usage is implied (read spend for the current period) and there is one conditional instruction: override the default workspace with workspaceId/workspaceSlug. But there is no guidance on when to choose this over related tools like luca_usage_messages, and no exclusions.

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