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

Annotations already declare readOnlyHint and idempotentHint, covering the safety profile. The description adds the null behavior for a zero starting value, which is not present in the schema or annotations. This is useful operational context that goes beyond the structured metadata.

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?

The description is two short sentences, immediately stating the core function and then the crucial edge case. Every word earns its place, with no redundant or extraneous information.

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 simple calculation tool with a complete input schema and an output schema present, the description covers the essential purpose and the key special case. No additional context is required for an agent to invoke it correctly.

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?

The input schema provides 100% coverage with descriptions for both 'from' and 'to'. The description's phrase 'from one value to another' simply mirrors the parameter names without adding new semantic detail, so it meets the baseline but adds no additional value.

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 uses a specific verb-like phrase ('Percentage change from one value to another') and clearly identifies the resource being calculated. It also adds a distinctive edge case (null for zero starting value), which distinguishes it from simple arithmetic tools and clarifies its scope.

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?

The description implies when to use the tool (whenever a percentage change between two values is needed) but does not explicitly state when not to use it or list alternatives. Given there are many financial calculation tools in the sibling set, more explicit differentiation would be helpful, but the simplicity of the operation makes the inference straightforward.

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