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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true), so the description's main contribution is the '(Cost: 1 credit)' notice, which is genuinely useful operational context not present in structured fields. It also clarifies that the response is an exact interval breakdown across multiple units, though it omits edge behavior such as reversed date order or invalid input handling.

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 short sentences, front-loaded with the core computation and then the required input format and cost. The opening 'Date Calculator: Date Calculator computes...' redundantly restates the title, a minor waste in an otherwise efficient definition.

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 two-parameter, read-only calculation tool with full schema coverage, an output schema, and annotations present, the description supplies what matters: the units returned, the required input format, and the credit cost. Only the absence of any sibling routing or edge-case handling keeps it from being fully complete.

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%, and both parameters already document the YYYY-MM-DD format with examples, so the schema carries the parameter burden. The description restates the format and the start/end ordering implication but adds no syntax or semantic detail beyond what is already structured; 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 and resource ('computes the difference between two calendar dates') and enumerates the output units (minutes through years), so the agent knows exactly what the tool returns. It lacks explicit differentiation from adjacent siblings such as AgeCalculator, WorkingDays, or JulianDayCalculator, leaving that inference to the agent.

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 usage through 'Supply start and end dates in YYYY-MM-DD format', which is enough to know the tool fits interval-difference questions. However, it gives no when-to-use vs. when-not guidance and never names an alternative for related tasks like age calculation or business-day counting.

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