Internet Issues- View allLast updated: 2026-03-30

System Development Contract Disputes in Japan: Defects and Breach of Contract

Key Takeaways

  • The 2020 Civil Code reform replaced "warranty against defects" with "non-conformity liability"
  • Courts recognize mutual cooperation obligations between vendors and users
  • Whether the contract is "contract for work" or "quasi-mandate" significantly affects liability
  • Notice of non-conformity must be given within 1 year of discovery

Types of System Development Contracts

Contract TypeObligationVendor Liability
Contract for Work (Civil Code Art. 632)Completion of the deliverableVendor bears completion responsibility
Quasi-Mandate (Art. 656)Performance of servicesNo completion obligation; duty of care only

In practice, multi-phase contracts are common: quasi-mandate for requirements definition and design; contract for work for development and testing.

2020 Civil Code Reform: Non-Conformity Liability

The April 2020 reform replaced "warranty against defects" (瑕疵担保責任) with non-conformity liability (契約不適合責任, Articles 562–564).

Key changes: - Applies regardless of whether the defect is "hidden" - Remedies expanded to include: cure demand (repair/replacement), price reduction, rescission, and damages

Notice Period

The buyer (user) must give notice within 1 year of discovering the non-conformity (Article 566).

Mutual Cooperation Obligations

Courts recognize that users also bear cooperation obligations. Where a user fails to clarify requirements or delays decisions, the vendor's liability may be reduced.

Common Disputes and Responses

Bug-ridden deliverable: Demand cure (repair) under Article 562; if refused, seek price reduction or rescission.

Project collapse: Claim damages for breach of contract (Article 415) under a contract for work; duty-of-care breach under quasi-mandate.

Unilateral additional fees: Under a contract for work, in-scope work cannot generate additional charges. Pre-agree on a change management process.

Key Contract Provisions to Include

  1. Requirements finalization procedure (signed agreement)
  2. Change management process (change request → estimate → approval)
  3. Acceptance criteria and timeline
  4. Liability cap clause
  5. Non-conformity liability period (e.g., 1 year from acceptance)

Summary

Most system development disputes stem from ambiguous requirements and unclear responsibility allocation. Addressing these contractually — with clear acceptance criteria, change management, and liability limitations — is the most effective prevention.

Free Tools for This Area

This article provides general legal information and does not constitute legal advice. For specific legal issues, please consult with a qualified attorney.

Related Articles

Related Q&A

Related Legal Terms

Find a lawyer through your local bar association

JFBA Legal Consultation Guide →