explain_cost_spike

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

With no annotations, the description carries the full burden and does disclose "Read-only" plus the analytical method (single day vs prior 7-day daily average, list-price basis). It does not say what happens when fewer than 7 days of history exist, whether the result is truncated to top-N drivers, or anything about response shape.

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 short sentences, each doing distinct work: scope, semantics, routing. The parenthetical date clarification is placed inline where it is needed and nothing is repeated from the name.

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 single-parameter, read-only analytical tool with no output schema, this is nearly complete — scope, comparison baseline, and date semantics are all covered. The only gap is the shape/granularity of the returned attribution (e.g. ranked list vs full breakdown).

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 0% and the schema only declares a bare string, so the description must compensate — and it does, pinning the format (YYYY-MM-DD), the timezone/billing-day semantics (UTC billing day), and the underlying field (system.billing.usage.usage_date).

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 and resource (explain a one-day cost spike) and immediately names the attribution dimensions (jobs/warehouses/clusters) plus the comparison basis (prior 7-day daily average). This is clearly distinct from cost_summary (aggregate) and top_cost_drivers (ranking) without opening either schema.

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?

Gives a concrete trigger ("why did Tuesday cost more?") and an explicit sequencing rule — use after cost_summary — which routes the agent relative to a sibling. It stops short of stating when NOT to use it (e.g. multi-day trend questions that belong to cost_summary or cost_review_report).

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