business-days-mcp

An MCP server for the date arithmetic that support, billing and operations teams actually do: is this a working day, when is this SLA due, what is the next working day after a bank holiday — plus cron and recurrence-rule parsing for the recurring side of the same job.

It runs offline. No network calls, no stored data, no model calls — every answer is computed from bundled public-holiday rules.

What it does

Business days and SLAs — holiday-aware for ~150 countries and their subdivisions (England and Scotland differ; so do US states), via the holidays package.

Cron and recurrence — parsing only. Nothing is scheduled, stored, or executed; there are no timers and no job store. If you want something run on a schedule, this is deliberately not that tool.

Related MCP server: mcp-chrono

Install and run

No install step needed — uvx fetches and runs it:

uvx --from git+https://github.com/Vessark/business-days-mcp business-days-mcp

From a clone:

git clone https://github.com/Vessark/business-days-mcp
cd business-days-mcp
uv sync && uv run business-days-mcp
uv run pytest                         # the tests are the documentation

Client configuration

Add to your MCP client's config (Claude Desktop, or anything that speaks MCP):

{
  "mcpServers": {
    "business-days": {
      "command": "uvx",
      "args": [
        "--from",
        "git+https://github.com/Vessark/business-days-mcp",
        "business-days-mcp"
      ]
    }
  }
}

Hosted

If you'd rather not run it, the same tools are available as a managed HTTP endpoint at https://vessark.com/mcp — no credentials needed for these:

{
  "mcpServers": {
    "vessark": {
      "url": "https://vessark.com/mcp"
    }
  }
}

Examples

// is_business_day — 2026-12-28, UK
{"date": "2026-12-28", "country": "GB"}
→ {"is_business_day": false, "reason": "holiday: Boxing Day (substitute day)"}

// sla_due_time — 8 business hours from Monday 16:00
{"start": "2026-07-27T16:00", "business_hours": 8}
→ {"due": "2026-07-28T16:00:00", "started_within_business_hours": true}

// explain_cron_expression
{"expression": "30 9 * * MON-FRI"}
→ {"explanation": "At 09:30, on Monday through Friday."}

Design notes

Every tool is a pure function of its arguments, which is why the test suite is mostly tables. Invalid input is an ordinary typed result, never an exception — a model that gets an argument wrong gets a readable reason and can correct itself. Every loop that a caller can influence is bounded, so no request can buy an expensive computation. Error messages never echo what you sent, so the server can't be used to relay text into someone else's agent.

Known limits, stated rather than hidden: a working week is Monday–Friday, so countries with Sunday–Thursday weeks are wrong under this assumption; holiday data covers only the years the underlying dataset knows about, and a date outside that range is refused rather than silently answered as an ordinary working day.

Releasing

Bump the version in both pyproject.toml and server.json, then push a matching tag:

git tag v0.2.0 && git push origin v0.2.0

That runs the test suite, checks the tag agrees with both version fields, and republishes to the MCP registry. Authentication is GitHub OIDC, so no token is stored anywhere.

About

Built and maintained by Vessark. The tools in this repository are the free tier and are open source under the MIT licence. Vessark's workspace tools — the ones that operate on a connected workspace — are the commercial product and are not open source.

Issues and pull requests welcome.