Observed arrival · 2026-09-02

Dierum, the calendar-aware date API

dierum.dev Observed source

Editorial interest 83/100 Selection signal · not a rating of the site

An API for business-day arithmetic, invoice due dates, payroll schedules, settlement dates, and holiday-aware deadlines.

Landing page captured for the 2026-09-02 issue.

Field notes

The homepage demonstrates date discrepancies through concrete calendar cases, including a Sunday invoice date, a Saudi Friday-Saturday weekend, and UK substitute holidays after Christmas falls on a Saturday. Its documented surface includes business-day arithmetic, invoice due-date rolling, rule-based paydays, and common working days across regions. The page links to language-specific materials for Python, JavaScript, and C#, plus an OpenAPI specification and llms.txt file.

Observed signals

Read the marks

Editorial observations of this landing page, not a rating.

○OpenPublic substance visible

$PaidCommerce or pricing visible

✦PrettyNotable craft visible

●ProPolished or operationally mature

◎NicheUnusually specific use

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