# Openworkdays

> Zero-signup business-day date-math API: add days, count days between dates, is-business-day.

- **Type:** MCP server
- **Install:** `agentstack add mcp-solvohq-openworkdays`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [SolvoHQ](https://agentstack.voostack.com/s/solvohq)
- **Installs:** 0
- **Category:** [Integrations](https://agentstack.voostack.com/c/integrations)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [SolvoHQ](https://github.com/SolvoHQ)
- **Source:** https://github.com/SolvoHQ/openworkdays

## Install

```sh
agentstack add mcp-solvohq-openworkdays
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# OpenWorkdays

**A zero-signup business-day / working-day date-arithmetic API. No account, no API key — one GET request.**

Add or subtract working days, count business days between two dates, or test
whether a date is a business day — with **your own** holiday list. Pure UTC date
math, returned as JSON. Built so autonomous AI agents get a deterministic date
endpoint — an agent has no human to do a signup, and LLMs are measurably
unreliable at date arithmetic.

Live: **https://openworkdays.vercel.app**

## Quick start

```sh
curl "https://openworkdays.vercel.app/api/businessdays?start=2026-05-15&days=5"
```

Sample response:

```json
{
  "mode": "add",
  "start": "2026-05-15",
  "days": 5,
  "result": "2026-05-22",
  "resultWeekday": "fri",
  "startIsBusinessDay": true,
  "weekend": ["sat", "sun"],
  "holidaysApplied": 0,
  "engine": "date-utc-v0.1",
  "computedAt": "2026-05-17T00:00:00.000Z"
}
```

Any error returns JSON with an `error` key and an appropriate HTTP status
(`400` bad params, `429` rate limited, `405` wrong method).

## The three modes

The endpoint is always `GET /api/businessdays`. The mode is inferred from the
params you pass.

### `add` — add/subtract working days

Params: `start=YYYY-MM-DD`, `days=N` (integer, `+`/`-` ok, `|N| <= 10000`),
optional `weekend=`, optional `holidays=`.

```sh
curl "https://openworkdays.vercel.app/api/businessdays?start=2026-05-15&days=5"
```

`N=0` returns `start` unchanged (even if `start` is itself non-working).

### `diff` — count business days between two dates

Params: `start=YYYY-MM-DD`, `end=YYYY-MM-DD`, optional `weekend=`, optional
`holidays=`. Inclusive of **both** endpoints. Result is negative if
`end` < `start`.

```sh
curl "https://openworkdays.vercel.app/api/businessdays?start=2026-05-15&end=2026-06-15&holidays=2026-05-25"
```

### `is` — is this date a business day?

Params: `date=YYYY-MM-DD`, optional `weekend=`, optional `holidays=`.

```sh
curl "https://openworkdays.vercel.app/api/businessdays?date=2026-05-16"
```

Returns `isBusinessDay` plus a `reason` of `"weekend"`, `"holiday"`, or `null`.

### Shared params

- **`weekend`** (default `sat,sun`) — comma list. Tokens are case-insensitive
  from `{sun,mon,tue,wed,thu,fri,sat}`, or numeric `0-6` where `0=Sunday` …
  `6=Saturday` (matches JS `getUTCDay()`). Cannot mark all 7 days as weekend.
- **`holidays`** — comma list of `YYYY-MM-DD` dates treated as non-working
  (max 1000). Strictly validated.

## Errors

Errors are JSON with an `error` key:

- `400` — bad/missing params (`missing start`, `invalid days (must be integer)`,
  `invalid weekend token`, `invalid holiday date`, `invalid date`,
  `specify a mode` (includes a `usage` object), …)
- `429` — rate limited (`Retry-After` header + `retryAfterSec`)
- `405` — wrong HTTP method (only `GET`/`OPTIONS` allowed)

## JavaScript

```js
const base = "https://openworkdays.vercel.app";
const r = await fetch(
  base + "/api/businessdays?start=2026-05-15&days=5"
);
const out = await r.json(); // { mode:"add", result:"2026-05-22", resultWeekday:"fri", ... }
```

## Use as an MCP tool (AI agents / Claude / Cursor / LLM clients)

OpenWorkdays is also a remote [MCP](https://modelcontextprotocol.io) server, so
an agent can call it as a tool with **no signup, no API key, no OAuth**.

- Endpoint: **`https://openworkdays.vercel.app/api/mcp`**
- Transport: **Streamable HTTP, stateless** (POST JSON-RPC 2.0, single
  `application/json` response — no sessions, no SSE)
- Exposes exactly one tool: **`businessdays`** — the mode (`add` / `diff` /
  `is`) is inferred from which args you pass, returning the same JSON as the
  REST endpoint (also as `structuredContent`)

Drop this into any MCP client config (Claude Desktop, Cursor, or any client
that speaks the Streamable HTTP transport):

```json
{ "mcpServers": { "openworkdays": { "url": "https://openworkdays.vercel.app/api/mcp" } } }
```

Quick smoke test:

```sh
curl -s -X POST https://openworkdays.vercel.app/api/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"businessdays","arguments":{"start":"2026-05-15","days":5}}}'
```

Over MCP, an upstream error comes back as a tool result with `isError: true`.

## Why

Every public business-day API gates behind an account or API key:
[workingdays.org](https://workingdays.org) is test-only / subscription;
[API Ninjas](https://api-ninjas.com) and [Holiday API](https://holidayapi.com)
need keys; [timeanddate](https://www.timeanddate.com) is a $299 product;
the RapidAPI business-day APIs need a RapidAPI key; Microsoft's "Calculate
Working Day" connector is Power-Platform-framework-gated and UK-bank-holidays
only. OpenWorkdays is a single anonymous `GET` — no signup, no key. That is
especially useful to autonomous agents, which have no human in the loop to
complete a signup. And because LLMs are measurably unreliable at date
arithmetic, an agent needs a deterministic endpoint rather than guessing.

## Limitations

- **Date-only, pure UTC arithmetic** — no time-of-day, no DST, no timezones
  (that is recurrence-rule territory, intentionally out of scope for v0.1).
- **Caller-supplied holidays only** — there is no built-in country holiday
  database. This is deliberate: we do not fake-compete on the
  7000-holiday-DB axis where funded incumbents win. You pass the
  `holidays=` list you care about.
- **Best-effort per-instance IP rate limit** — a soft abuse brake, not a
  guarantee (serverless instances are ephemeral and not shared).
- **MIT licensed and self-hostable** — see below.

## Self-host — it's zero-dependency files

The entire API is two single zero-dependency Node serverless functions:
[`api/businessdays.js`](api/businessdays.js) (REST) and [`api/mcp.js`](api/mcp.js)
(remote MCP). No `npm install`, no deps at all. Deploy the folder to Vercel
(zero-config `/api` detection) or drop the handlers into any Node serverless
runtime.

```sh
git clone https://github.com/SolvoHQ/openworkdays
cd openworkdays
npx vercel --prod
```

## License

MIT — see [LICENSE](LICENSE).

## Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [SolvoHQ](https://github.com/SolvoHQ)
- **Source:** [SolvoHQ/openworkdays](https://github.com/SolvoHQ/openworkdays)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** yes
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/mcp-solvohq-openworkdays
- Seller: https://agentstack.voostack.com/s/solvohq
- Browse the marketplace: https://agentstack.voostack.com/browse

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