# Bizday

> Bizday 0.3.2. Verified US business calendars for agents. The default is us-federal-opm. us-fed-banking is the Federal Reserve Banks schedule: a Saturday holiday does not close Friday. Dates are civil dates (YYYY-MM-DD). Not legal, payroll, or financial advice.

Coverage is 2021-01-01 through 2100-12-31. Omit the calendar query parameter and the calendar is us-federal-opm. Unknown calendar ids return 400 invalid_calendar. There is no API key. Years after 2030 use the same rules and are not a copy of a later official table.

On 2026-07-03, `us-federal-opm` is not a business day and `us-fed-banking` is a business day. One business day after 2026-07-02 is 2026-07-06 on `us-federal-opm` and 2026-07-03 on `us-fed-banking`. roll with direction next: moves from 2026-07-03 to 2026-07-06 on `us-federal-opm` (reason `observed federal holiday`), and stays on 2026-07-03 on `us-fed-banking`.

add matches Excel WORKDAY: the start date is day 0, so days=1 always leaves the start date. diff matches Excel NETWORKDAYS: both ends count when they are business days. roll stays on a business day and otherwise moves to the nearest one. direction is next or previous. roll is not WORKDAY, and it does not decide whether a filing is timely.

Every calculation response includes calendar, sources, and disclaimer. Inauguration Day is reported on the office calendar and is not a nationwide closing. It is not a Reserve Bank holiday. us-fed-banking is not the Board of Governors Friday closure when a holiday falls on Saturday, and it is not ACH or Fedwire operating hours.

Preview traffic is 60 requests per minute per IP on the calculation routes and on MCP tool calls. GET /v1, GET /v1/health, GET /openapi.json, GET /llms.txt, GET /.well-known/mcp.json, and GET /.well-known/mcp/server-card.json are not counted. MCP initialize, ping, server/discover, and tools/list are not counted.

Paths in the lists below are root-relative. The OpenAPI server URL is https://isitabizday.com.

## Calendars

- [us-federal-opm](/v1/calendars): US federal offices (OPM Monday–Friday). Default when calendar is omitted. Saturday: Observed the preceding Friday (5 U.S.C. § 6103(b)(1)). Sunday: Observed the following Monday (Executive Order 11582 § 3(a)). Source: https://www.opm.gov/policy-data-oversight/pay-leave/federal-holidays/. Last verified 2026-10-17.
- [us-fed-banking](/v1/calendars): Federal Reserve Banks and Branches. Saturday: Banks stay open the preceding Friday. The Board of Governors is closed that Friday. K.8. Sunday: Banks and the Board of Governors are closed the following Monday. K.8. Source: https://www.federalreserve.gov/aboutthefed/k8.htm. Last verified 2026-10-17.

## Contract

- [OpenAPI](/openapi.json): OpenAPI 3.1 for these two calendars. Server URL is https://isitabizday.com. Examples are live responses, including the 2026-07-03 contrast. Operation ids: get_health, list_calendars, list_holidays, is_business_day, add_business_days, count_business_days, roll_date.
- [MCP](/.well-known/mcp.json): POST JSON-RPC to https://isitabizday.com/mcp (streamable HTTP, no session). Protocol versions 2026-07-28, 2025-11-25, 2025-06-18, and 2025-03-26. Tools: is_business_day, add_business_days, count_business_days, roll_date, list_holidays, list_calendars.
- [MCP server card](/.well-known/mcp/server-card.json): serverInfo, the same tools as tools/list, empty resources, and empty prompts. No auth. Not rate limited.
- [Service index](/v1): Version, coverage, endpoint list, and the paths of this file, the OpenAPI document, MCP, and the server card. Not rate limited.

## Tools

- [get_health](/openapi.json): GET /v1/health. Liveness. Not rate limited.
- [list_calendars](/openapi.json): GET /v1/calendars. Id, name, source URL, Saturday and Sunday rules, coverage, last verified, and changelog.
- [list_holidays](/openapi.json): GET /v1/holidays?year=YYYY. The eleven nationwide legal holidays. On us-fed-banking, observed is null when the legal date is a Saturday, because Friday stays open.
- [is_business_day](/openapi.json): GET /v1/business-days/check?date=YYYY-MM-DD. Optional calendar. Whether the date is a business day, why, and the previous and next business days.
- [add_business_days](/openapi.json): GET /v1/business-days/add?start=YYYY-MM-DD&days=N. Excel WORKDAY shape: the start date is day 0. days is an integer from -3660 to 3660.
- [count_business_days](/openapi.json): GET /v1/business-days/diff?start=YYYY-MM-DD&end=YYYY-MM-DD. Excel NETWORKDAYS shape: both ends count. Negative when end is earlier.
- [roll_date](/openapi.json): GET /v1/business-days/roll?date=YYYY-MM-DD&direction=next. direction is next or previous. Stays put when the date is already a business day. This is not Excel WORKDAY, and it does not decide whether a filing is timely.

## Optional

- [Human docs](/): The same facts as HTML. Curl samples on that page use a BIZDAY variable.
- [Privacy](/privacy.html): No accounts and no cookies. No contact address is published yet. Checkout is off.