Datecalc

Add Duration

add_duration

Read-onlyIdempotent

Add (or subtract, with negatives) a duration to a date and return the new UTC date/time. Provide any of years/months/weeks/days/hours/minutes/seconds.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "date": "2025-01-01T00:00:00Z",
      "days": 15,
      "months": 6
    },
    "name": "add_duration"
  }
}

Input Schema

Name	Required	Description
`date`	Yes	Base date/time (ISO-8601).
`days`	No
`hours`	No
`weeks`	No
`years`	No
`months`	No
`minutes`	No
`seconds`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJul 29, 2026

addedInput schema / examples

Added value: +[
+  {
+    "date": "2025-01-01T00:00:00Z",
+    "days": 15,
+    "months": 6
+  },
+  {
+    "date": "2025-06-30",
+    "hours": -3,
+    "years": 1
+  }
+]

First observedJul 1, 2026

TDQS

A4/5.0

Behavior4/5

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

The description adds that it returns a UTC date/time and supports subtraction via negative values. Annotations already provide readOnlyHint, idempotentHint, etc., so the description adds moderate context without contradiction.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences: first states the primary function and return value, second enumerates the parameters. Every word contributes, no fluff, and it is front-loaded with the key action.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 8 parameters, no output schema, and informative annotations, the description covers the core behavior. It lacks details on parameter combination behavior and exact precision, but is sufficient for a straightforward duration calculator.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 13% (only 'date' has a description). The description lists the duration parameter names (years, months, etc.), adding some meaning, but does not specify constraints, ranges, or default values. It partially compensates for the low coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action (add or subtract duration) and the resource (a date), and specifies the return of a new UTC date/time. It distinguishes itself from sibling tools like date_diff and date_info by focusing on duration arithmetic.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies the usage scenario (adding/subtracting durations) but does not explicitly mention when not to use it or suggest alternatives among sibling tools. There is no guidance on prerequisites or exclusions.

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

All Datecalc tools Inspect

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