Calculate the number of days between two dates by subtracting Date B from Date A. Use it to measure date spans for scheduling, billing, or project timelines.
Return the number of days between two dates (a - b).
| Name | Required | Description | Default |
|---|---|---|---|
| date_a | Yes | ||
| date_b | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v1.0.4Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full disclosure burden. It does disclose the operand order and therefore the sign of the result ('a - b'), which is genuine behavioral information. However, it says nothing about accepted date formats, timezone handling, or error behavior for unparseable input — meaningful gaps for a date tool.
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?
A single short sentence that front-loads the operation and closes with the operand order. No filler, nothing to trim.
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?
An output schema exists, so return-value explanation is not required. But for a tool whose only inputs are date strings, omitting the expected format leaves a real operational gap that the description should have closed.
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 description coverage is 0%, so the schema only supplies bare titles ('Date A', 'Date B'). The description compensates partially by defining the subtraction direction, mapping date_a to the minuend and date_b to the subtrahend. It still leaves the required string format (e.g. ISO 8601 vs epoch) unspecified.
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 ('Return the number of days between two dates') and adds the operand order '(a - b)', which separates it from datetime_add_days and other datetime siblings. It is clear, though it never explicitly names or excludes an alternative tool.
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?
There is no when-to-use statement, no prerequisites, and no mention of the closely related datetime_parse or datetime_add_days siblings. The agent must infer from the name alone that this is the difference operation.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.