SKILL.md Lint

Cron Explain

cron_explain

Read-onlyIdempotent

Explain a 5-field cron expression in plain English and flag mistakes. FREE.

Typical input {"expression": "0 9 * * 1-5"} returns {"expression": "0 9 * * 1-5", "meaning": "at minute 0; at hour 9; every day of month; every month; day of week 1-5", "issues": ["none"]}; out-of-range fields are listed in "issues".

Use to read a schedule back in plain English before trusting it. Assumes 5-field cron; not for 6-field or seconds-precision variants. Errors: on invalid, missing, or malformed input this tool never raises a protocol error; it returns {"error": ""} (for example {"error": "expected 5 fields, got "}). Every call is read-only and idempotent, so after correcting the input it is always safe to retry.

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": {
      "expression": "<expression>"
    },
    "name": "cron_explain"
  }
}

Input Schema

Name	Required	Description	Default
`expression`	Yes	A standard 5-field cron string (minute hour day-of-month month day-of-week), e.g. "0 9 * * 1-5"; must be non-empty.

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedAug 17, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already declare read-only, idempotent, non-destructive behavior, but the description adds important error semantics: it never raises a protocol error and returns an error object with corrective guidance. It also describes the success response shape and issue reporting, going beyond the annotation metadata.

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

Conciseness4/5

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

The description is front-loaded with the purpose and example output, followed by usage constraints and error behavior. Most sentences carry weight, though the promotional "FREE." is unnecessary and the response example slightly overlaps the output schema.

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?

The tool has rich annotations, full schema coverage, and an output schema, and the description still fills remaining gaps around unsupported cron variants and error handling. An agent has enough information to invoke it correctly and understand what happens on bad input.

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%, and the schema already documents that the input must be a non-empty standard 5-field cron string. The description reinforces the 5-field assumption and gives an example, but adds little parameter meaning beyond what the schema already provides, so the baseline 3 applies.

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?

States a specific verb and resource: "Explain a 5-field cron expression in plain English and flag mistakes." It also explicitly excludes 6-field and seconds-precision variants, so an agent can distinguish the scope without opening the schema.

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

Usage Guidelines5/5

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

Gives a clear use case: "Use to read a schedule back in plain English before trusting it." It also states the key exclusion: "Assumes 5-field cron; not for 6-field or seconds-precision variants." This covers both when to use it and when not to use it.

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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