Japanese Construction AI Releases 20 Real Cost Diagnoses, Exposing Overcharges Up to $19,600
The Horizons Co., Ltd. published an open dataset of 20 construction cost reviews on May 18, 2026, documenting overcharges ranging from $2,450 to $19,600 across Japanese renovation and new-build projects. The cases span 15 prefectures and 20 construction categories, from exterior painting to seismic reinforcement.
The average overcharge detected was $5,775. A termite extermination job in Chiba Prefecture showed the highest fraud rate: 84.9%, with a quoted price of ¥1,850,000 against a fair-market estimate of ¥280,000.
The dataset is available under CC-BY 4.0 licensing on GitHub, with both HTML and JSON formats. Each case includes a 12-character cryptographic audit hash for independent verification.
Blockchain Anchoring and Methodology Transparency
The company anchored its diagnostic protocol to Bitcoin Block #949356 on May 14, 2026, using the OpenTimestamps service. The SHA-256 hash of the protocol declaration is publicly verifiable on the blockchain, allowing contractors and homeowners to confirm the methodology unchanged.
Toshikatsu Oga, the company's representative director, said the anchoring addresses a core problem: "A diagnostic methodology that cannot be independently verified loses credibility at the negotiation table."
Who's Behind This
Oga spent more than 30 years in construction before transitioning to AI engineering. He began a carpentry apprenticeship at age 15 in 1993 and worked in on-site supervision and project management. His direct experience informed the company's focus on cost overcharges - he observed that 20% markups or higher are routine in renovation contracts.
The underlying research is published through Zenodo and engrXiv under open-access terms, with a formal database (JCCDB v1.2.2) available for peer review.
The Service and Pricing
HORIZON SHIELD offers three core diagnostics:
- Construction cost review: ¥55,000
- Change-order assessment: ¥33,000
- On-site completion inspection: ¥88,000
A reverse-estimate PDF report costs ¥5,500 for early-stage budget planning. The tool is accessible via web and through the ChatGPT GPT Store.
Regulatory Alignment
The Horizons Co. voluntarily adopted design principles from the EU AI Act, specifically around record-keeping and human oversight, despite the system not being classified as high-risk under the regulation.
The company commits to directing a portion of HORIZON SHIELD revenue to Médecins Sans Frontières (MSF).
For professionals managing construction contracts or overseeing renovation budgets, the open dataset provides a reference point for evaluating contractor estimates. Learn more about AI for Real Estate & Construction applications in cost analysis and verification.
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