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

Annotations already establish a safe read-only profile, but the description adds important behaviour: results are rounded to 6 decimal places, malformed expressions are refused with a reason, series evaluations cap at 2000 steps, and the tool is free and requires no design. These are meaningful operational details beyond the structured annotations.

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 dense and front-loaded with the core purpose. The long function list is useful for a calculator, though the prose could be slightly more structured; almost every clause earns its place.

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?

Given a five-parameter tool with nested objects, no output schema, and rich annotations, the description covers invocation modes, return shapes, limits, error behaviour, and usage context. It gives an agent everything needed to call the tool 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?

Schema coverage is 100%, so the baseline is 3, but the description adds useful mode semantics: one expression returns result, named expressions can reference earlier names, and series evaluation returns values as [x, y] pairs. It does not need to repeat every schema detail, but it helpfully clarifies the three invocation patterns.

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 opens with a specific verb and resource: 'Evaluate arithmetic exactly instead of estimating,' then lists supported operators and functions. It clearly distinguishes this tool from estimation and from sibling helpers like place_items and stagger_times.

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?

It gives explicit use cases (sizes, positions, angles, colour contrast) and names alternatives for related tasks: design_guide for contrast formulas, place_items for many item positions, and stagger_times for start times. This is enough for an agent to choose correctly.

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