Chrono MCP Server

chrono-mcp

The MCP server for time math at scale. Batch-crunch up to 100,000 timestamps in a single tool call, speak the industry's temporal interchange standards (RFC 9557 IXDTF, RFC 5545 RRULE, ISO 8601 repeating intervals), and give your agent a passive sense of passing time on every response. Powered by Luxon, DST-correct by construction, and every limit is benchmark-backed.

Quick Start

npx @jmoak/chrono-mcp

Run as local HTTP server

npm install
npm run build
npm run start:http
# Server listens on http://localhost:8000/mcp (health check at /health)

MCP Client Configuration

Configure your MCP client to launch chrono-mcp via npx. Below are client-specific examples.

Claude Code

Ask Claude! Here's the configuration:

{
  "mcpServers": {
    "chrono-mcp": {
      "command": "npx",
      "args": ["-y", "@jmoak/chrono-mcp@latest"]
    }
  }
}

Cursor

Reference: Cursor MCP docs

{
  "mcpServers": {
    "chrono-mcp": {
      "command": "npx",
      "args": ["-y", "@jmoak/chrono-mcp@latest"]
    },
    "chrono-mcp-http": {
      "type": "http",
      "url": "http://localhost:8000/mcp"
    }
  }
}

Why chrono-mcp

LLMs are famously bad at time: they miscount weekdays, lose track of elapsed time between turns, and fall apart on DST math. chrono-mcp fixes all three — and does it at bulk scale, in the formats the rest of the industry already speaks.

• Bulk by design - 10,000 calculations per request for per-item operations; 100,000 timestamps for stats, which returns pure aggregates. Every cap is proven by a benchmark you can run yourself (npm run bench) — per-item ops finish in under 100ms at the cap, 100k-item stats in ~460ms
• RFC 9557 (IXDTF) Interchange - All datetime inputs accept bracketed IANA zone annotations (2026-08-09T15:00:00-04:00[America/New_York]) with Temporal-compatible offset-consistency validation, plus an ixdtf output format — the serialization standard of the JS Temporal API
• Recurrence Expansion - expand turns RFC 5545 RRULEs (the format Google Calendar, Outlook, and Apple Calendar store) and ISO 8601 repeating intervals into concrete occurrences — DST-correct, window-bounded, with explicit truncation reporting
• Temporal Context Envelope - Every tool response carries a compact trailing line with the current time, weekday, elapsed time since the agent's previous call, session age, and tzdb version — passive time-awareness on every interaction
• Batch Error Isolation - One bad timestamp doesn't sink a 10,000-item batch: invalid entries are skipped and reported (invalid_count + samples), never silently dropped
• Token-Optimized Output - Dynamically shaped responses that maximize information density while minimizing token usage
• Global Timezone Support - All IANA timezone identifiers, with ISO, RFC2822, SQL, and locale-aware formatting
• Type Safety - Zod validation on every parameter, MCP-compliant errors, strict TypeScript throughout

Documentation

• API Reference - Complete documentation of all tools, parameters, and examples
• Architecture - System architecture and design principles
• Examples - Practical usage examples and patterns

Available Tools

GET TIME

Get current time or convert times across timezones with flexible formatting.

Parameters:

• datetime (string, optional): ISO datetime string. Defaults to current time
• timezones (array, optional): List of timezone names for conversions
• formats (array, optional): Output formats (iso, rfc2822, sql, local, localeString, short, medium, long, full)
• locale (string, optional): Locale for formatting (e.g., en-US, fr-FR, ja-JP)
• includeOffsets (boolean, optional): Include UTC offsets in output

Example:

Input

{
  "datetime": "2024-01-01T12:00:00Z",
  "timezones": ["America/New_York", "Asia/Tokyo"],
  "includeOffsets": true
}

Output

{
  "baseTime": "2024-01-01T12:00:00.000Z",
  "America/New_York": "2024-01-01T07:00:00.000-05:00",
  "Asia/Tokyo": "2024-01-01T21:00:00.000+09:00"
}

TIME CALCULATOR

Perform time arithmetic at any scale — single conversions to 100k-item batch analysis.

Operations:

• add - Add duration to a datetime
• subtract - Subtract duration from a datetime
• diff - Calculate simple difference in various units
• duration_between - Detailed duration breakdown between two times
• stats - Statistical analysis of time series and durations (up to 100,000 timestamps per call)
• sort - Sort timestamps chronologically
• expand - Expand an RFC 5545 RRULE or ISO 8601 repeating interval into occurrences

Every operation accepts arrays as well as single values, with interaction_mode controlling how base and compare arrays combine (pairwise, cross_product, single_to_many, …). Invalid entries in a batch are skipped and reported — never silently dropped, never fatal.

Expand example:

Input

{
  "operation": "expand",
  "recurrence": "FREQ=WEEKLY;BYDAY=TU;COUNT=4",
  "base_time": "2026-02-24T09:00:00[America/New_York]",
  "occurrence_format": "ixdtf"
}

Output (result excerpt — note the wall-clock time held across the DST transition)

{
  "rule_type": "rrule",
  "count": 4,
  "truncated": false,
  "occurrences": [
    "2026-02-24T09:00:00.000-05:00[America/New_York]",
    "2026-03-03T09:00:00.000-05:00[America/New_York]",
    "2026-03-10T09:00:00.000-04:00[America/New_York]",
    "2026-03-17T09:00:00.000-04:00[America/New_York]"
  ]
}

Also accepts ISO 8601 repeating intervals (R5/2026-03-01T14:00:00Z/P1D), window_start/window_end bounds, and max_occurrences caps (default 100, max 10,000) with explicit truncated reporting.

Bulk stats example — hand it your entire event log; the response stays tiny no matter how many timestamps go in (up to 100,000):

{
  "operation": "stats",
  "base_time": ["2026-01-01T00:00:00Z", "...99,998 more...", "2026-01-02T03:46:39Z"]
}

Output (aggregates only — real excerpt from a 100,000-timestamp call that ran in ~500ms)

{
  "input_analysis": { "base_time_count": 100000 },
  "timestamp_analysis": {
    "earliest": "2026-01-01T00:00:00.000Z",
    "latest": "2026-01-02T03:46:39.000Z",
    "total_span_human": "1 day, 3 hours, 46 minutes, 39 seconds",
    "std_deviation_ms": 28867513
  },
  "interval_analysis": {
    "interval_count": 99999,
    "mean_interval_human": "1 second"
  }
}

Parameters:

• operation (required): Type of calculation
• interaction_mode (optional): auto_detect | single_to_many | many_to_single | pairwise | cross_product | aggregate. Defaults to auto_detect.
• base_time (optional): Base ISO datetime(s). String or array. Defaults to current time.
• compare_time (optional): Compare ISO datetime(s) for diff/duration_between. String or array.
• timezone (optional): Timezone for base_time
• compare_time_timezone (optional): Timezone for compare_time
• years, months, days, hours, minutes, seconds (optional): Duration values

Example:

Input

{
  "operation": "add",
  "base_time": "2024-12-25T10:00:00Z",
  "days": 5,
  "hours": 3
}

Output

{
  "operation": "add",
  "interaction_mode": "single_to_single",
  "input": {
    "base_time": "2024-12-25T10:00:00.000Z",
    "duration": { "days": 5, "hours": 3 }
  },
  "result": "2024-12-30T13:00:00.000Z",
  "result_timezone": "UTC"
}

Temporal Context Envelope

Every tool response includes a second content block — a single ~20-token line giving the calling agent passive time-awareness:

⏱ now 2026-08-09T15:02:11.123-04:00 (Sun) · first call this session
⏱ now 2026-08-09T15:49:03.456-04:00 (Sun) · +46m52s since last call · session 47m1s · call #2

LLMs have no innate sense of elapsed time between turns; the envelope makes time passage visible on every interaction with the server — including the weekday, which models frequently miscompute. Disable it by setting CHRONO_ENVELOPE=off in the server environment.

Prerequisites

• Node.js >= 22.0.0
• npm or yarn

Setup

git clone https://github.com/yourusername/chrono-mcp.git
cd chrono-mcp
npm install

Build

npm run build

Testing & Inspector

npm test
npm run test:ui
npm run test:mcp
npm run inspector

npm run bench

• npm test — Vitest unit tests for tool handlers
• npm run bench — Vitest benchmarks proving every batch operation at the MAX_OPERATIONS cap (10,000 items) completes in well under 100ms
• npm run test:mcp — Vibrissa (npm: @jmoak/vibrissa) MCP protocol cases (requires npm run build first; no Python)
• Protocol contracts live in tests/contracts/*.tdd and emit to tests/integration/vibrissa/cases/ via tdd-dsl locally (npm run contracts:emit if tdd-dsl is on your PATH). CI runs only the committed JSON with vib run.

Visit http://localhost:6274 for the web inspector UI.

Linting

npm run lint
npm run lint:fix

Supported Timezones

Supports all IANA timezone identifiers including:

• Americas: America/New_York, America/Los_Angeles, America/Toronto, etc.
• Europe: Europe/London, Europe/Paris, Europe/Berlin, etc.
• Asia: Asia/Tokyo, Asia/Shanghai, Asia/Dubai, etc.
• Australia: Australia/Sydney, Australia/Melbourne, etc.
• And 400+ more...

Acknowledgments

This project is powered by Luxon, the excellent DateTime library that provides robust timezone handling and date arithmetic. We're grateful to the Luxon team for creating such a reliable foundation for temporal operations.

License

MIT License - see the LICENSE file for details.

Releases

See GitHub Releases for detailed changes.