# business-days-mcp

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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`](https://pypi.org/project/holidays/) package.

| Tool | Answers |
| --- | --- |
| `is_business_day` | Is this a working day? If not, is it a weekend or a named holiday? |
| `next_business_day` / `previous_business_day` | The next/last working day around a date |
| `add_business_days` | Move ±N working days from a date |
| `business_days_between` | How many working days between two dates (half-open) |
| `first_business_day_of_month` / `last_business_day_of_month` | Month boundaries |
| `sla_due_time` | When does an N-business-hour SLA fall due, counting only open hours? |

**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.

| Tool | Answers |
| --- | --- |
| `validate_cron_expression` / `explain_cron_expression` | Is this cron valid, and what does it mean in English? |
| `next_cron_occurrences` | When would it next fire? |
| `validate_recurrence_rule` / `explain_recurrence_rule` | Same, for an RFC 5545 RRULE |
| `next_recurrence_occurrences` | Expand an RRULE to its next occurrences |

## Install and run

The hosted endpoint needs no install at all — see
[Client configuration](#client-configuration). To run it yourself, `uvx`
fetches and runs it:

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

From a clone:

```sh
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

### Hosted — nothing to install

The quickest way in. The same tools, no install, no credentials:

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

### Run it yourself

If you would rather not depend on someone else's uptime, run it locally —
it is the same code, and it never touches the network:

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

## Examples

```jsonc
// 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.

## Prior art

[`fbdo/business-day-mcp`](https://github.com/fbdo/business-day-mcp) covers
business-day and holiday arithmetic and predates this server. If that is all
you need, use it — it also exposes timezone-aware "today" and holiday listing,
which this server does not.

This one was built for a different centre of gravity: **SLA clocks** that count
only business hours, and **cron / RRULE parsing** for the recurring side of the
same work. The overlap in the business-day tools is real and the names are
conventional; both servers are MIT licensed and both build on the excellent
[`holidays`](https://pypi.org/project/holidays/) package.

## Releasing

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

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

That runs the test suite, checks the tag agrees with both version fields,
publishes to PyPI, and republishes to the MCP registry. Both use GitHub OIDC —
PyPI via Trusted Publishing — so there is no API token in this repository, in a
secret store, or on any machine.

## About

Built and maintained by [Vessark](https://vessark.com). 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.