DATA API
Japan's public data, in a form AI can use directly
We rebuild tables and registries published by Japan's public bodies into APIs that AI agents and software can use in a single call. Our sources include the National Tax Agency (NTA), the Japan Health Insurance Association (Kyokai Kenpo), the Ministry of Health, Labour and Welfare (MHLW), the Cabinet Office, and gBizINFO from the Ministry of Economy, Trade and Industry (METI). Since before our founding, Kasanegi has built and offered a family of these data APIs. We are now integrating that family into a single foundation that brings all of Kasanegi's work together. In the meantime, so that you can try the real thing, one example from the family is open to everyone: the ten APIs of JP Local Pack, free of charge with no sign-up. We also hold further data APIs for company records and grants, and open more of them as our AI resources grow.
AN EXAMPLE · JP LOCAL PACK
One example: Japanese back-office work in ten APIs
This example from our family of data APIs is open free of charge today. Running payroll, checking business partners, validating invoices: the calculations and checks that Japanese companies repeat every month, packaged so that AI can call them directly.
| API | Returns | Source |
|---|---|---|
Payroll summary/combined/payroll-summary | From a monthly salary: each insurance premium, withholding income tax, total deductions and take-home pay, plus that month's national holidays | Kyokai Kenpo, MHLW, NTA, Cabinet Office |
Payroll deductions/payroll/calc-by-salary | Health insurance, long-term care insurance, child and child-rearing support contribution, employees' pension, employment insurance, withholding income tax and take-home pay | Kyokai Kenpo, Japan Pension Service, MHLW, NTA |
Standard monthly remuneration/social-insurance/standard-remuneration | Grade and premium across the 50 health insurance grades and 32 employees' pension grades | Kyokai Kenpo, Japan Pension Service |
Consumption tax rate/tax/consumption/rate | Standard and reduced rates for any date, and whether that date falls on or after the start of the Qualified Invoice System | NTA |
National holidays/holiday/jp | National holidays, substitute holidays and citizens' holidays for 2024–2027, with English names | Cabinet Office |
Company search by name/houjin-lookup/by-name | Candidate corporate numbers for a company name, with the evidence that tells them apart | gBizINFO (METI) |
Corporate number lookup/houjin-number/lookup | A company overview from its corporate number | gBizINFO (METI) |
Invoice issuer search/invoice/issuer-by-name | Whether a company, found by name, is registered as a qualified invoice issuer | gBizINFO, NTA published data |
Invoice registration lookup/invoice/issuer-registration-lookup | Registration status and date from a registration number (T number) | NTA Qualified Invoice Issuer Publication Site (published data) |
Peppol validation/invoice/peppol-validate | Validation results for invoice data against 15 key rules of Peppol BIS Billing JP | Peppol BIS Billing JP |
Prefix each path with https://api.kasanegi.com/preview/v1/local (the table shows the rest of the path).
ACCURACY
Matched to the official tables, to the yen
In payroll, close is not good enough. We carry the official tables and rules exactly as published.
- Withholding income taxWe carry all 1,856 cells of the Kō column of the monthly table in the NTA's Withholding Tax Table for Employment Income (2026): 231 brackets × 0 to 7 dependants, plus the bottom row. Our tests confirm that every cell matches the official table. When monthly pay after social insurance deductions is ¥740,000 or more, tax is computed with the formulas for nine brackets, as the table's notes specify. Results also match the worked examples in the NTA's guide to using the monthly table.
- Health and long-term care insuranceWe carry Kyokai Kenpo's FY2026 rates for all 47 prefectures, and check grades, ranges and premiums against all 50 rows of the Tokyo premium table. Fractions of a yen follow the table's notes: amounts of 0.50 yen or less are rounded down, and amounts over 0.50 yen are rounded up. For employees aged 40 to 64, health insurance and long-term care insurance are added together before rounding.
- Support contribution, pension, employment insuranceWe cover the child and child-rearing support contribution on pay from April 2026 (0.23%), employees' pension (18.3%), and employment insurance (general businesses: employee share 5/1,000, applied to wages rather than standard remuneration, with fractions handled as the rules specify).
- Consumption taxWe carry the full rate history by effective date, from 3% in 1989 to the 10% standard and 8% reduced rates of October 2019. The API also determines whether a date falls on or after the start of the Qualified Invoice System (1 October 2023), with dates decided in Japan time.
- Invoice registryWe build the registry from the NTA's complete published data and its updates, with 5,009,701 registrations ready to look up. Every response carries the as-of date of its data.
- National holidaysFrom Cabinet Office data: 75 days from 2024 to 2027, covering national holidays, substitute holidays and citizens' holidays.
- ¥50,390
- total deductions on a ¥300,000 monthly salary, Tokyo, age 30 (take-home pay ¥249,610)
- ¥113,596
- withholding income tax on a ¥1,050,000 monthly salary, Tokyo, age 45 (formula for ¥740,000 or more)
- 1,856 cells
- checked against the NTA monthly table, every one a match
TRY
Call it now, no sign-up
No key, no registration. Call it straight from your browser or the command line.
curl "https://api.kasanegi.com/preview/v1/local/payroll/calc-by-salary?monthly_salary=300000&pref_code=13&age=30"200 Monthly salary ¥300,000 · Tokyo (pref_code=13) · age 30
- health_insurance_employee
- 14,775
- child_care_support_employee
- 345
- pension_employee
- 27,450
- employment_insurance_employee
- 1,500
- income_tax_withholding
- 6,320
- total_deduction
- 50,390
- net_salary
- 249,610
Each client can make up to 30 calls every 60 seconds. For heavier business use, you can get a key on RapidAPI, an API marketplace for developers.
FOR AI AGENTS
Use with AI agents
Through our MCP server, AI agents can discover all ten as tools, along with how to use each one and where to call it. We also publish the API definition (OpenAPI 3.1) and a guide for AI (llms.txt). The product list, the API definition and the tool list are all generated from a single registry, so they agree wherever you look.
- MCP server
https://mcp.kasanegi.com/mcp(Streamable HTTP · MCP 2025-06-18)- API definition
https://api.kasanegi.com/openapi.json(OpenAPI 3.1)- Guide for AI
https://api.kasanegi.com/llms.txt- Product list
https://api.kasanegi.com/products
SOURCES
Data sources
| Data | Provided by |
|---|---|
| Withholding Tax Table for Employment Income (2026) | National Tax Agency (NTA) |
| Insurance rates and premium tables by prefecture (FY2026) | Japan Health Insurance Association (Kyokai Kenpo) |
| Employees' pension insurance premium rate | Japan Pension Service |
| Employment insurance premium rates (FY2026) | Ministry of Health, Labour and Welfare (MHLW) |
| Consumption tax rates | National Tax Agency (NTA) |
| National holidays | Cabinet Office |
| Basic corporate information (gBizINFO) | Ministry of Economy, Trade and Industry (METI) |
| Published data on qualified invoice issuers | National Tax Agency (NTA) |
| Peppol BIS Billing JP | OpenPeppol, Digital Agency |
HISTORY
Milestones
- Release
Opened the ten APIs of JP Local Pack free of charge with no sign-up, as one example while we integrate our family of data APIs
- Listing
Our data API family was listed in a developer community's directory of APIs for AI agents
- Release
Launched kasanegi.com and released our data APIs, also listing them on RapidAPI, an API marketplace for developers
- Release
Released Japanese public data as APIs that AI can use directly
To discuss adopting our data APIs or building them into your operations, contact us at contact@kasanegi.com.