agent-toolbelt

Cron Expression Builder

build_cron

Convert natural language schedule descriptions into cron expressions for automated task scheduling. Provides expression, human-readable confirmation, and next run times.

Instructions

Convert natural language schedule descriptions into cron expressions. Examples: 'every weekday at 9am', 'first Monday of each month at noon', 'every 5 minutes'. Returns the expression, human-readable confirmation, and next 5 run times.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "description": "<description>"
    },
    "name": "build_cron"
  }
}

Input Schema

Name	Required	Description	Default
`description`	Yes	Natural language schedule description
`timezone`	No	Timezone for context	UTC

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Mar 30, 2026

TDQS

A4.5/5.0

Behavior4/5

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

With no annotations, description carries full burden and successfully discloses return structure (expression, confirmation, next 5 run times) compensating for missing output schema. Omits error handling or rate limits, but 'convert' implies safe, idempotent operation appropriate for this tool class.

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?

Two efficiently structured sentences: first states core function with illustrative examples, second discloses return format. Front-loaded, no redundant words, every clause earns its place.

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

Completeness5/5

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

For a simple 2-parameter conversion tool without output schema, description adequately covers input expectations via examples and output structure via explicit return value listing. No gaps requiring additional clarification given the low complexity.

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

Parameters4/5

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

Schema coverage is 100%, establishing baseline 3. Description adds significant value by providing concrete input examples ('every 5 minutes') that clarify expected natural language patterns beyond the schema's generic 'Natural language schedule description' label.

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?

Clear specific verb 'Convert' identifies the transformation (natural language → cron expressions). Distinct from sibling 'build_regex' by resource type (schedules vs patterns) and clearly scoped to cron generation.

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

Usage Guidelines4/5

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

Provides clear context through three concrete input examples ('every weekday at 9am', etc.), implicitly indicating when to use the tool. Lacks explicit 'when-not' or alternative naming, though no direct cron-building sibling exists requiring differentiation.

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