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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real value by specifying the change is 'simple' percentage change (i.e., not CAGR or compounded), but it omits the key edge case for this operation — what happens when previous_value is zero.

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?

One front-loaded sentence that leads with the computation. The trailing clause ('including sales or revenue growth and percentage increase or decrease') is largely redundant restatement of 'percentage change' and could be cut.

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?

Simple, well-annotated, fully described schema — little is needed. But with no output schema, the description should state the return convention (percentage points like 25 vs a fraction like 0.25, and whether a decrease is negative), which is exactly the ambiguity that causes misuse of a change calculator.

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 both numeric inputs and the 'comparison' enum are already documented, including that the enum is label-only. The description only restates 'between 2 values' and adds no ordering, sign convention, or scaling detail beyond the schema — baseline 3 applies.

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 ('calculates') and resource ('simple percentage change between 2 values') and enumerates the comparison types it covers (YoY, MoM, QoQ, WoW). An agent knows exactly what computation happens, but the description never distinguishes this from siblings like growth_rate or ytd_growth, which plausibly overlap.

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 through example scenarios ('sales or revenue growth', 'percentage increase or decrease'). There is no explicit when-to-use, no exclusion, and no routing away from growth_rate, ytd_growth or growth_projection, which are the most likely confusions in this sibling set.

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