cron-check

Explain and check cron expressions

explain_cron

Read-onlyIdempotent

Explain cron expressions in plain English, validate syntax, identify dialect and gotchas, detect never-firing schedules, and preview next 3 UTC runs.

Instructions

Explains up to 20 cron expressions in plain English and checks them: valid or why not, the dialect, gotchas (day-of-month OR day-of-week, uneven steps, GitHub's 5-minute floor), schedules that never fire, and the next 3 runs in UTC.

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": {
      "expressions": "<expressions>"
    },
    "name": "explain_cron"
  }
}

Input Schema

Name	Required	Description	Default
`dialect`	No	detected when omitted
`expressions`	Yes

Output Schema

Name	Required	Description	Default
`results`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 26, 2026

TDQS

A4.3/5.0

Behavior5/5

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

The annotations already declare the tool read-only, idempotent, and non-destructive. The description goes beyond that by disclosing concrete behavioral details: it handles up to 20 expressions, reports validity and reasons, identifies dialect, surfaces known gotchas, detects never-firing schedules, and returns the next 3 runs in UTC. This gives the agent a rich picture of what the tool will do.

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 sentence that front-loads the core action ('Explains up to 20 cron expressions in plain English') and then uses a compact colon-separated list to enumerate behaviors. Every phrase adds information, and the structure makes the tool's scope immediately scannable.

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?

Given the output schema exists and the annotations cover safety/idempotence, the description covers the essential invocation context: input limits, validation behavior, dialect handling, known edge cases, and return content. No critical behavioral aspect needed for selecting or calling the tool is missing.

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 50%: the dialect parameter is described ('detected when omitted') while expressions is not. The description adds some meaning by mentioning the 20-expression limit and that the tool checks dialect, but it does not fully compensate for the undocumented expressions parameter or explain how the dialect input relates to the output. The schema and description together are adequate but not comprehensive.

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 uses specific verbs ('explains', 'checks') tied to a clear resource ('cron expressions') and enumerates concrete outputs: validity, dialect, gotchas, never-firing schedules, and next runs. This content also distinguishes it from siblings like convert_cron and next_runs by showing it performs explanation and validation, not just conversion or run calculation.

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 clearly implies when to use the tool—whenever a cron expression needs explanation or validation—but it does not explicitly state when not to use it or name alternatives such as convert_cron or next_runs. There is no direct routing guidance, so the agent must infer the boundary from the feature list.

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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