API Tool Calls

Hours Calculator

hours_calculator

Read-onlyIdempotent

Calculate worked minutes, decimal hours and H:MM from clock times, an overnight flag and an unpaid break.

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": {
      "end": "06:00",
      "start": "22:00",
      "overnight": true,
      "breakMinutes": 30
    },
    "name": "hours_calculator"
  }
}

Input Schema

Name	Required	Description
`end`	Yes	End clock time HH:MM (24-hour)
`start`	Yes	Start clock time HH:MM (24-hour)
`overnight`	No	End is on the next day; shift at most 24 hours
`breakMinutes`	No	Unpaid break in whole minutes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 4, 2026

TDQS

B3.4/5.0

Behavior3/5

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

Annotations already declare the full safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description carries a light burden. It adds that the break is unpaid and that the calculation depends on the overnight flag, but discloses no computation edge cases, rounding rules, or limits beyond what the schema already states (e.g. max 24 hours).

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?

A single 20-word sentence, front-loaded with the verb and the outputs. No filler, no repetition; every clause maps to a real part of the tool's contract.

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?

For a simple deterministic calculator with 100% schema coverage, an output schema, and annotations covering safety, the description supplies enough to call it correctly. The one real omission is disambiguation from time_card_calculator, which an agent facing this sibling set would benefit from.

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 description coverage is 100% with all four parameters documented, so the baseline is 3. The description restates the same four inputs (clock times, overnight flag, unpaid break) without adding format, range, or interaction semantics beyond the schema, such as what happens when the computed shift crosses midnight without the overnight flag.

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

Purpose4/5

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

States a specific verb (calculate) and concrete outputs (worked minutes, decimal hours, H:MM) from identifiable inputs (clock times, overnight flag, unpaid break). An agent can tell this is a shift-duration calculator. However, it does not distinguish itself from the very similar sibling time_card_calculator, which also produces hours worked from clock times.

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

Usage Guidelines2/5

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

There is no when-to-use guidance, no exclusions, and no routing to alternatives. This matters here because time_card_calculator sits in the sibling list doing an overlapping job, and the description gives the agent no basis for choosing between them.

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

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