Japan public-data APIs for AI agents.

The three products

Each product lists the buyer job, the best first preview call (free), the paid production path, a price range, and a real example of what the call returns.

curl -sS "https://api.kasanegi.com/preview/v1/local/combined/payroll-summary?monthly_salary=300000&year_month=2026-05"

# End buyers should use the published marketplace listing, not curl this
# origin path directly. The marketplace proxy injects the shared secret.
curl -i \
  -H "X-Kasanegi-Marketplace-Secret: <set-by-marketplace-proxy>" \
  "https://api.kasanegi.com/marketplace/rapidapi/v1/local/combined/payroll-summary?monthly_salary=300000&year_month=2026-05"

# 402 without X-PAYMENT; settle and retry with X-PAYMENT (open x402 protocol).
curl -i "https://api.kasanegi.com/v1/local/combined/payroll-summary?monthly_salary=300000&year_month=2026-05"

{
  "monthly_salary": 300000,
  "year_month": "2026-05",
  "income_tax_jpy": 6850,
  "health_insurance_jpy": 14760,
  "pension_jpy": 27450,
  "employment_insurance_jpy": 1800,
  "net_pay_jpy": 249140,
  "_attribution": "NTA / MHLW / Kyokai Kenpo (public official sources)"
}

curl -sS "https://api.kasanegi.com/preview/v1/enrich/company-by-name?name=%E3%83%88%E3%83%A8%E3%82%BF%E8%87%AA%E5%8B%95%E8%BB%8A"

# End buyers should use the published marketplace listing, not curl this
# origin path directly. The marketplace proxy injects the shared secret.
curl -i \
  -H "X-Kasanegi-Marketplace-Secret: <set-by-marketplace-proxy>" \
  "https://api.kasanegi.com/marketplace/rapidapi/v1/enrich/company-by-name?name=%E3%83%88%E3%83%A8%E3%82%BF%E8%87%AA%E5%8B%95%E8%BB%8A"

# 402 without X-PAYMENT; settle and retry with X-PAYMENT (open x402 protocol).
curl -i "https://api.kasanegi.com/v1/enrich/company-by-name?name=%E3%83%88%E3%83%A8%E3%82%BF%E8%87%AA%E5%8B%95%E8%BB%8A"

{
  "candidates": [
    {
      "corporate_number_hint": "<13-digit corporate number>",
      "legal_name": "<resolved legal name>",
      "match_reliability": 0.98,
      "match_reliability_label": "high",
      "_source": "gBizINFO + brand alias map"
    }
  ]
}

curl -sS "https://api.kasanegi.com/preview/v1/grants/detail?id=a0WJ200000CDYZ2MAP"

# End buyers should use the published marketplace listing, not curl this
# origin path directly. The marketplace proxy injects the shared secret.
curl -i \
  -H "X-Kasanegi-Marketplace-Secret: <set-by-marketplace-proxy>" \
  "https://api.kasanegi.com/marketplace/rapidapi/v1/grants/detail?id=a0WJ200000CDYZ2MAP"

# 402 without X-PAYMENT; settle and retry with X-PAYMENT (open x402 protocol).
curl -i "https://api.kasanegi.com/v1/grants/detail?id=a0WJ200000CDYZ2MAP"

{
  "grant_id": "<j-grants-id>",
  "title": "<grant title>",
  "deadline_date": "<YYYY-MM-DD>",
  "max_subsidy_amount_jpy": "<integer or null>",
  "amount_extraction_status": "ok | ambiguous_upstream | unknown",
  "data_completeness_score": 0.82,
  "_attribution": "Digital Agency J-Grants PDL 1.0"
}

What we do not promise

• Sources are public official or public-registry sources only (J-Grants, gBizINFO, EDINET, NTA, Cabinet Office, MHLW, Kyokai Kenpo). No private or pre-disclosure data.
• Outputs are reference data or review-required candidates. We do not give legal, payroll, KYB, tax, or grant-eligibility final decisions.
• Builder: MatsushitaTokitsugu, Japan. https://api.kasanegi.com is the single buyer integration target.

Sales channels

x402 is one option, not the only one. Production access is not gated on holding crypto.

• Marketplace / API-key path — buy through a marketplace listing (RapidAPI-class provider proxy) when that product has a public listing. Pay by card or platform credit, no crypto required. Origin route: https://api.kasanegi.com/marketplace/rapidapi/v1/{local|enrich|grants}/.... Status: One public marketplace listing is live for all current products at https://rapidapi.com/kasanegi123/api/jp-local-pack-japan-payroll-invoice-tax-apis..
• x402 direct micropayment — settle USDC on Base mainnet per call, for agent-native buyers. Origin route: https://api.kasanegi.com/v1/{local|enrich|grants}/....
• Card / fiat checkout (Stripe / Polar / equivalent) — not yet wired. Owner must create the merchant account and configure pricing.
• Wallet-free preview — https://api.kasanegi.com/preview/v1/{local|enrich|grants}/.... Same JSON shape as paid path; for evaluation only, not a paid path.

Full machine manifest with per-channel status: /products (sales_channels) and /.well-known/broker-manifest.json.

Developers and agents

If you would rather meter against a free trial, get a wallet-free key:

curl -sS -X POST https://api.kasanegi.com/keys/create \
  -H "content-type: application/json" \
  -d '{"owner_label":"my-team"}'

curl -sS -X POST https://api.kasanegi.com/broker/call \
  -H "X-API-Key: <key>" \
  -H "content-type: application/json" \
  -d '{"product_id":"jp-local-pack-v1-combined-payroll-summary","query":{"monthly_salary":300000,"year_month":"2026-05"}}'

Machine-readable surfaces:

• /products — JSON product catalog (with sales_channels)
• /openapi.json — OpenAPI 3.1 (with marketplace_rapidapi paths)
• /llms.txt — LLM guide
• /.well-known/x402 — x402 auto-discovery (one channel of many)
• /supported — x402scan-compatible alias
• /portal.md — Markdown portal for LLM readers
• /feedback/schema — buyer feedback schema
• MCP gateway for agent clients