Platform-user agreements generally seek to regulate long-term relationships in a highly detailed manner, whilst retaining the operator’s commercial capacity to maintain and develop the Platform. Accordingly, unilateral variation clauses are core elements of the private governance of platform ecosystems. Whilst the contemporary growth of diversity in platform structures can manifest in more diverse user terms, e.g. in integrated or collaborative platforms, the core capacity to steer the contractual relationship generally remains with the operator. This is arguably necessary for the business efficacy of digital platforms in an increasingly complex legal and economic landscape. However, despite their prevalence, such terms remain a borderline feature of contract law, challenging doctrinal conceptions of contract as a static, bilateral consensus and raising questions of validity and interpretation. Invalidity is only likely where terms breach explicit regulatory standards, or provide an imbalance that is unconscionable or unfair under established contractual doctrine. Whilst regulatory protections exist for some users at an EU level, these remain relatively formalistic and limited in scope. Nonetheless, validity does not imply unlimited use of unilateral variation clauses. Contractual interpretation is influenced by the regulatory framework, which imposes systemic expectations of general business conduct in digital markets, establishing standards of objectivity and appropriateness. In non-intermediary platform settings, where regulatory protection is more limited, interpretation inspired by principles of administrative law and derived from the nature and purpose of the contract may restrict the operator’s discretion. Though not unfamiliar to contemporary contract law, such standards are complex and outcomes will rely heavily on specific circumstances.