Techum Shabbos Calculatorתחום שבת — about this project

Our goal & mission

Establishing a techum Shabbos today is almost entirely manual work: someone traces buildings on a map by hand, measures gaps one by one, squares the city by eye, and publishes a line that is hard for anyone else to check. Existing tools stop at drawing a rectangle you position yourself. The derivation itself — which buildings count, which chains join at 70⅔ amos, which settlements merge at 141⅓, where the ribua and the 2000-amos boundary actually fall — is exactly where mistakes happen, and exactly what nobody had automated.

This project's goal is to make that derivation fast, transparent, and checkable for any address in the world, so that a rav or mumcheh reviewing a techum spends their time on the halachic judgment calls — not on tracing rooftops. It is decision-support for a posek, never a replacement: the Mishna Berurah (399:7) requires techum measurement by an expert, and every output of this tool carries that banner permanently.

Principles

• Every rule cites its source. The full halachic spec below records each rule, each machlokes, and each open question, with references — nothing is a black box.
• Every disputed rule is a setting. Defaults follow the widely-known psak (Mishna Berurah / Ashkenazi profile); genuinely split machlokes are offered as options (Chazon Ish, Mechaber/Sefardi profiles), never silently decided.
• Deterministic and auditable. Same map data + same settings = the same line, every time. Snapshots freeze data, settings, and manual decisions into a file a rav can review, approve, and replay exactly. Every export embeds the full configuration and data provenance.
• Human review is the product. Map data is imperfect and dwelling status is a halachic judgment. Uncertain buildings are flagged in color, one click includes or excludes them, and the line recomputes instantly. The audit-rings display draws the actual 70⅔-amos distances on the map so every join can be verified by eye.
• Both audiences. A layperson gets sensible locked defaults and clear warnings; a rav gets the full configuration matrix and review tools.

Privacy: this site keeps self-hosted usage statistics—including page visits, addresses searched, calculation locations, settings, coarse country, and device information—to understand what is useful and where the tool needs work. Raw events are retained for 12 months; non-identifying daily totals may be retained indefinitely. Raw IP addresses are not stored in the analytics database. A rotating keyed network identifier is used for abuse prevention and expires with the raw event. The private analytics dashboard is restricted with Cloudflare Access.