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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds two useful pieces beyond that — a plan gate ('Unlimited plan') and the exact metric set returned — but does not explain what happens on insufficient data or how the comparison window handles the change date itself.

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 sentences with essentially no filler, and the core comparison logic is stated up front. The leading fragment 'Unlimited plan.' is terse to the point of ambiguity but does carry gating information, so it earns its place despite the abrupt placement.

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?

With no output schema, the description usefully names the three returned metrics so the agent knows what comes back, and the fully described schema covers the inputs. The main remaining gap is edge-case behavior — short windows, unavailable historical data, or whether statistical significance is reported.

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 all four parameters are already documented, which sets the baseline at 3. The description does add interpretive meaning to change_date and days by framing them as a symmetric before/after window around the change day, but adds nothing about login_customer_id or bounds handling.

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 states a specific analytical operation: comparing spend, conversions and cost per conversion before and after the day a change was applied, which is far more informative than the opaque name 'did_it_work'. It does not, however, name or contrast with siblings like change_history or campaign_performance, which could also surface pre/post numbers.

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 only implied: the agent can infer it should call this after applying a change to measure impact. There is no explicit 'use this instead of X' guidance and no statement of preconditions, such as whether the change must first appear in change_history or how recent change_date may be.

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