Adversarial interoperability

Working Definition

Adversarial interoperability (also termed competitive compatibility or comcom) is the practice of creating a new product or service that plugs into, reads the file formats of, or interfaces with an existing dominant system against the wishes and without the permission of that system's owner: reverse-engineering a proprietary protocol, building an alternative third-party client, refilling a chipped printer cartridge, or stripping ads and trackers from a webpage. Introduced by Cory Doctorow in 2019, the concept contrasts this practice with indifferent interoperability (where a manufacturer does not care who makes accessories, like a standard wall socket) and cooperative interoperability (where firms voluntarily agree on a shared standard or open API). While casual shorthand sometimes equates it with “consumer-friendly hacking,” analytically it describes a legal-technical regime in which clean-room reverse engineering, bots, scrapers, and format converters are protected from intellectual-property and computer-crime liability, allowing insurgents to overcome network effects by piggybacking on an incumbent's installed base.

Genesis and Global Lineage

The phrase was coined by Cory Doctorow in a series of essays on the Electronic Frontier Foundation (EFF) Deeplinks blog between June and October 2019—calling it “an elegant weapon for a more civilized age”—and expanded into a policy program in Chokepoint Capitalism (with Rebecca Giblin, 2022) and The Internet Con (2023). Doctorow's core historical argument is that today's tech monopolies were themselves built through adversarial interoperability before kicking away the ladder: in the 1980s, Phoenix Technologies and Compaq used clean-room reverse engineering to clone the IBM PC BIOS; Andrew Tridgell's Samba reverse-engineered Microsoft's SMB protocol so Linux servers could join Windows workgroups; Apple built iWork to read and write Microsoft .doc files without Redmond's blessing; and Facebook scaled early on by providing tools that scraped users' messages and friend lists out of MySpace. Intellectually, the concept synthesizes the cyberlaw tradition of Lawrence Lessig (Code, 1999), Pamela Samuelson and Suzanne Scotchmer (The Law and Economics of Reverse Engineering, 2002), and Jonathan Zittrain (The Future of the Internet, 2008). Doctorow argues that this generative dynamic was strangled after 1998 by a legal thicket—Section 1201 of the US Digital Millennium Copyright Act (DMCA) banning DRM circumvention, the Computer Fraud and Abuse Act (CFAA) treating terms-of-service violations as felony hacking, software patents, and clickwrap licenses—which turned unauthorized compatibility into a crime. Since 2020, Doctorow has also used the synonym competitive compatibility (comcom) so policymakers do not mistake pro-consumer competition for cyberwarfare.

Central European Lineage

We found no documented link between this concept and the intellectual history or historical experience of Central Europe.

Why Now

Between 2019 and 2026, the question of who may legally plug into a dominant platform moved to the center of technology regulation. In 2019, the expert report Competition Policy for the Digital Era (by Jacques Crémer, Yves-Alexandre de Montjoye, and Heike Schweitzer) placed interoperability on the European Commission's agenda, leading to the EU Digital Markets Act (DMA, enforced from 2024), which requires designated “gatekeepers” to open messaging services (such as WhatsApp) and mobile operating systems (such as iOS) to third-party app stores and payment systems. Doctorow entered this debate with a warning: top-down mandates alone let incumbents game standards committees, whereas legalizing bottom-up adversarial interoperability lets nimble competitors route around foot-dragging gatekeepers. Simultaneously, high-profile flashpoints dramatized the struggle: the “Right to Repair” movement battling John Deere over encrypted tractor diagnostics and Apple over parts pairing; Twitter/X and Reddit shutting down free API access in 2023 to kill third-party clients like Apollo; Apple blocking Beeper Mini in December 2023 after it reverse-engineered iMessage for Android users; and the rise of federated social networks (Mastodon/ActivityPub, Bluesky/AT Protocol) designed to prevent any company from locking in the social graph.

Explanatory Power

Adversarial interoperability explains why network effects alone do not make digital monopolies immortal—and why legal shields, rather than superior engineering, keep users trapped. First, it exposes the “ladder-kicking” pattern of Silicon Valley history: nearly every dominant platform used unpermissioned scraping, protocol emulation, or format conversion when it was a challenger, then lobbied for strict anti-circumvention and anti-scraping laws once it became the incumbent. Second, it shows that switching costs are a policy choice rather than a law of physics: leaving Facebook or WhatsApp feels impossible today because leaving means losing contact with friends who stay behind; if an independent client were legally permitted to read and write messages into Facebook's network without Meta's consent, a user could leave the company without leaving the community. Third, it illuminates the hidden danger of complex compliance mandates: when governments impose duties that only a trillion-dollar incumbent can automate, and allow that incumbent to invoke “security compliance” to block third-party clients, regulation inadvertently cements the monopoly's moat.

Axes of Debate

Underappreciated Angle

Although adversarial interoperability is usually discussed as a concept in software engineering or antitrust law, at its deepest level it is a struggle over where the boundary of private property ends. In twentieth-century manufacturing, the doctrine of exhaustion (or the first-sale doctrine) drew a bright legal line at the point of purchase: once you bought a car, a tractor, or a toaster, the manufacturer's property right in that object was exhausted, and any independent mechanic or parts maker had the right to open the hood, study how the bolts fitted together, and manufacture a compatible spare part without asking permission. By embedding encrypted microchips and copyrighted firmware into physical goods—from printer cartridges and insulin pumps to John Deere tractors and iPhone screens—and wrapping every digital service in a restrictive license rather than a sale, corporations shifted the legal boundary from the physical object to the interface. Once the interface is protected by anti-circumvention felonies, ownership dissolves into revocable tenancy. Crucially, after 2023 this legal battle flipped polarity in generative AI: the very tech giants that spent two decades using the CFAA and terms of service to outlaw small developers from scraping their walled gardens invoked a sweeping right to unpermissioned scraping when devouring the open web to train their proprietary foundation models—while locking those models behind strict terms that forbid anyone else from distilling or interoperating with them. Asking “who has the right to adversarial interoperability?” exposes this double standard immediately.