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Japanese holidays, business days, eras, postal codes, addresses and corporate numbers.
Remote server: your requests and data go to biz.ossalt.jp. Claude Code: claude mcp add --transport http japan-business-tools https://biz.ossalt.jp/mcp · Claude app: Settings → Connectors → Add custom connector.
The tools this server listed when we connected to it, in its own words.
list_holidays — List all Japanese national holidays and substitute holidays for a year, based on the National Holidays Act and verified against the Cabinet check_business_day — Check whether a date is a business day in Japan, and if not, why (weekend, holiday name, bank closure, or a custom closed day). `reason` is add_business_days — Return the date that is N business days after (or before, if N is negative) the given date. The start date itself is not counted; e.g. 1 buscount_business_days — Count business days from start to end, inclusive of both ends. Returns 0 if start is after end. The period can be up to 3,660 days (about 10adjust_to_business_day — If the date is a business day, return it as is; otherwise move to the next ("next") or previous ("previous") business day. Useful for paymenlast_business_day_of_month — Return the last business day of the given month. / その月の最終営業日。to_japanese_era — Convert a Gregorian date (YYYY-MM-DD) to the Japanese era calendar, e.g. 2026-10-07 → 令和8年10月7日 (wareki_short R8.10.07, zero-padded). Year 1from_japanese_era — Convert a Japanese era date to YYYY-MM-DD. Accepts 令和8年10月7日, 令和元年5月1日, R8.10.7, H31/4/30, Reiwa 8.10.7, kanji numerals (昭和六十四年一月七日), a trailookup_postal_code — Look up the address (prefecture, city, town) for a 7-digit Japanese postal code, from Japan Post data. Accepts forms like 1000001, 100-0001 search_postal_code — Find Japanese postal codes by prefecture, city and (optionally) part of the town name, from Japan Post data. The city must be the full municnormalize_address — Split a Japanese address into prefecture, city, town and the rest (block numbers, building), matching Japan Post's address data, and return lookup_corporate_number — Look up a 13-digit Japanese corporate number (法人番号) in the National Tax Agency's monthly bulk data: name, furigana, English name, kind, regisearch_corporation_by_name — Find Japanese corporations whose name starts with the given text (prefix match), in the National Tax Agency's monthly bulk data. Legal-form Not tested by KitScout yet. When our harness runs it, pros, cons and the tasks we tried appear here, with the date and evidence.