Design Language Control as a Form of Market Power

1. Introduction

Design language refers to the visual, functional and interaction conventions through which a digital product communicates with users. It includes buttons, menus, icons, colours, labels, defaults, rankings, navigation structures, notifications, prompts, terminology, recommendation layouts, APIs, and other elements of user-interface and user-experience (UI/UX) design.

Traditionally, competition law has focused on price, output, market share, contracts, exclusivity and access to essential inputs. In digital markets, however, control over design itself can become an instrument of market power.

A dominant platform may not need to prohibit competitors directly. It can influence competition by deciding:

• where competing services appear;
• which option is presented as the default;
• how many steps are required to switch;
• which terminology users encounter;
• which products receive visual prominence;
• whether rival services receive equivalent functionality;
• how warnings and consent screens are framed;
• whether interoperability is technically or visually inconvenient;
• whether users can easily discover alternatives; and
• how the platform's own services are integrated into the interface.

The European Commission's recent digital-market enforcement illustrates this development. For example, in 2026 the Commission found Google had given its own services preferential prominence in Search, including through enhanced visuals and filters, while also addressing Google's restrictions on steering users toward alternative purchasing channels.

Thus, design language can operate as a competitive infrastructure, not merely as aesthetics.

2. Meaning of Design Language Control

Design language control exists when a firm with substantial market power has the ability to determine the rules through which users perceive, navigate and interact with competing products or services.

It can be divided into several forms.

A. Visual control

The platform determines:

• colour;
• size;
• position;
• prominence;
• icons;
• badges;
• labels;
• typography; and
• visual hierarchy.

For example, placing the platform's own service at the top of a search page while competitors appear lower can influence consumer choice even when competitors remain technically available.

B. Navigational control

A platform can make its own service easier to reach.

Example:

Platform service → one click
Rival service → four menus → warning → confirmation → external webpage.

The rival has not necessarily been formally excluded, but the cost of choosing the rival has been increased.

C. Default-setting control

Defaults are particularly powerful because many users do not change them.

Examples include:

• default browser;
• default search engine;
• default payment mechanism;
• default map application;
• default voice assistant;
• default cloud service; and
• default app-store payment channel.

The UK's CMA has specifically been examining Google's presentation of consumer choices and “choice architecture” in general search.

D. Linguistic control

Language itself can influence competition.

Examples:

• “Recommended” for the dominant firm's service;
• “Other options” for rivals;
• “Continue” for accepting the dominant firm's choice;
• “Change settings” for selecting an alternative;
• warnings suggesting that switching is unsafe;
• terminology that makes the firm's product appear to be the natural or official option.

Thus, semantic framing can have competitive consequences.

E. Functional design control

The platform may design its ecosystem so that its own service works more seamlessly.

For example:

Platform-owned app → automatic login + notifications + OS integration + payment integration

while:

Rival app → additional permissions + manual authentication + restricted APIs + limited notifications.

The difference may arise from technical restrictions rather than explicit contractual exclusion.

The DMA's interoperability requirements recognise this problem by requiring designated gatekeepers to provide third parties access to certain OS features available to the gatekeeper's own services.

3. Why Design Can Constitute Market Power

Design becomes particularly important where the platform has:

1. high market share;
2. strong network effects;
3. significant user data;
4. high switching costs;
5. strong brand recognition;
6. control over an operating system;
7. control over an app store;
8. control over search rankings;
9. control over essential APIs; or
10. an ecosystem that users find costly to leave.

The fundamental economic problem is choice architecture combined with market power.

A competitive market normally allows consumers to discover and compare alternatives.

If a dominant intermediary controls the mechanism through which alternatives are discovered, it may influence competition before the consumer even reaches the point of comparing products.

4. Design Control and Self-Preferencing

One of the most important applications is self-preferencing.

Suppose a platform operates both:

• a marketplace; and
• a competing seller/service.

It controls the interface.

It may give its own service:

• a larger tile;
• higher ranking;
• richer graphics;
• automatic recommendations;
• default placement;
• special badges;
• additional filters; or
• pre-installed status.

The rival may technically remain accessible, but the competitive environment is altered.

The European Commission's 2026 Google Search decision provides a particularly direct contemporary example: the Commission stated that Google gave its own services preferential treatment through greater prominence, including placement at the top of results and enhanced visuals and filters.

5. Design Language and Exclusionary Conduct

The legal question is not simply:

“Is the design unfair?”

Competition law instead asks whether the design forms part of conduct capable of restricting competition.

Relevant considerations include:

1. Dominance

Is the undertaking sufficiently powerful that users or competitors cannot realistically bypass its interface?

2. Intent

Evidence of deliberate design choices may be relevant, although competition liability does not necessarily depend upon proving subjective intention.

3. Foreclosure

Does the design reduce the ability of rivals to compete effectively?

4. Consumer dependence

Are users accustomed to the dominant interface?

5. Switching costs

Does changing the interface or default require substantial effort?

6. Replicability

Can competitors realistically reproduce the dominant platform's design environment?

7. Counterfactual

Would competition be materially different if rival services received equivalent visibility and functionality?

6. Dark Patterns as a Related Concept

Dark patterns represent the consumer-protection dimension of design control.

They involve interface structures that may:

• obscure important information;
• make cancellation difficult;
• steer consumers toward a particular option;
• use confusing language;
• exploit default choices; or
• create unnecessary friction for rejecting an offer.

The FTC has described dark patterns as interface designs capable of obscuring, subverting or impairing consumer autonomy and choice.

The important distinction is:

Dark-pattern regulation primarily protects consumers; competition law asks whether design control affects competitive conditions.

The same interface can potentially implicate both bodies of law.

7. Major Case Laws

Case 1: Google Search (Shopping) — Google Search and Shopping

The European Commission's Google Shopping case is highly relevant because it demonstrates how ranking and presentation can influence competition.

Google operated a general search engine while also offering its own comparison-shopping service.

The Commission found that Google systematically gave prominent placement to its comparison-shopping service while applying less favourable positioning to competing comparison-shopping services.

The significance for design-language theory is that the alleged competitive harm did not depend simply upon denying competitors access to Google Search. Instead, the architecture of visibility and ranking affected discoverability.

Principle

A dominant intermediary's control over the presentation of competing services may become an instrument of exclusion where it systematically disadvantages rivals.

8. Case 2: Google Android — Google LLC v European Commission, T-604/18

The Android litigation concerned Google's conduct involving Android, Google Search, Chrome, Play Store and agreements with manufacturers and mobile network operators.

The General Court examined Google's broader ecosystem strategy, including product tying, exclusivity arrangements and anti-fragmentation obligations.

The importance for design-language analysis is that competition in an operating-system ecosystem is not merely about the operating system's technical code.

It also involves:

• pre-installation;
• defaults;
• app availability;
• interoperability;
• ecosystem integration;
• search access; and
• user expectations created by the interface.

Principle

Control over the architecture of an ecosystem can reinforce market power across adjacent digital services.

9. Case 3: Microsoft — Microsoft Corp. v Commission

The Microsoft cases concerning Windows and competing technologies remain foundational for understanding design-based ecosystem power.

Microsoft's control over the Windows operating-system environment gave it the ability to determine how complementary technologies interacted with the dominant operating system.

The case is important because it demonstrates that technical architecture and interoperability can have competitive significance.

The broader lesson is:

When a dominant undertaking controls an important technological environment, design decisions concerning compatibility may affect the ability of competitors to enter or remain in neighbouring markets.

This provides an important conceptual foundation for modern API, operating-system and interface disputes.

10. Case 4: Epic Games v Apple

The dispute between Epic Games and Apple concerned Apple's App Store ecosystem and restrictions surrounding app distribution and payments.

The case raised questions concerning Apple's control over:

• app distribution;
• payment mechanisms;
• developer rules;
• user access;
• alternative purchasing arrangements; and
• the structure through which developers reach iOS users.

Although not every issue in the litigation is properly characterised as “design language,” the dispute demonstrates why interface architecture and ecosystem rules can interact.

If a platform controls the point through which consumers encounter and purchase competing products, the design and functionality of that point can influence competitive opportunities.

Principle

Control of the consumer-facing gateway can confer economic significance on seemingly ordinary interface decisions.

11. Case 5: Epic Games v Google

The Epic Games litigation against Google similarly concerned the Android ecosystem, Google Play and payment/distribution arrangements.

Its relevance to design-language analysis lies in the relationship between:

• technical architecture;
• consumer discovery;
• payment pathways;
• app distribution;
• platform rules; and
• alternative channels.

The case illustrates that competition analysis in digital ecosystems increasingly requires attention to how the platform structures the consumer journey, not simply the price charged by the platform.

12. Case 6: FTC v Amazon — Amazon Prime

The FTC's Amazon Prime litigation provides an especially direct example of interface-based conduct.

The FTC alleged that Amazon used manipulative interface designs—described as dark patterns—to enroll consumers into Prime and make cancellation difficult.

The FTC specifically alleged that Amazon's cancellation process was structured in a manner designed to impede cancellation.

Although this is principally a consumer-protection case rather than a conventional Article 102/competition-law dominance case, it is highly relevant to the theory of design as economic power.

Principle

Control over interface architecture can materially influence consumer behaviour even without changing the underlying price or contractual product.

The competition-law question is then whether similar design control also disadvantages competing firms.

13. Case 7: Apple — Browser Choice Screen under the DMA

The European Commission opened proceedings concerning Apple's browser-choice screen because of concerns that the design might prevent users from genuinely exercising their choice of browser.

The Commission subsequently closed the investigation after Apple changed the browser-choice experience, including by streamlining the process for selecting and setting a new default browser.

This is particularly important because it demonstrates a regulatory shift from asking merely:

“Is another browser technically available?”

toward asking:

“Can the user realistically exercise the choice?”

Principle

Formal availability is not necessarily equivalent to effective contestability.

A competitor can be technically available but commercially disadvantaged if the dominant interface makes selecting it unusually difficult.

14. Case 8: Google Search and Digital Markets Regulation

The UK's contemporary Google Search regulatory process provides another important development.

The CMA has designated Google as having Strategic Market Status in general search and search advertising and has been developing conduct requirements concerning consumer choice and choice architecture.

The CMA's 2026 consultation specifically addresses how Google presents choices and influences consumer decision-making.

This is significant because choice architecture itself is becoming a regulatory object.

15. Design Language as a Barrier to Entry

Design control can create entry barriers in several ways.

A. Discovery barrier

A new entrant exists but consumers rarely see it.

B. Trust barrier

The dominant platform labels its own service as “verified”, “recommended” or “official”.

C. Switching barrier

Changing from the incumbent requires several steps.

D. Compatibility barrier

The rival cannot access equivalent functionality.

E. Learning-cost barrier

Consumers are familiar with the incumbent's design language and would need to learn a different system.

F. Attention barrier

The dominant platform occupies the user's limited attention before competitors are encountered.

16. Design Language and Network Effects

Design language can amplify network effects.

Suppose 90% of users understand Platform A's interface.

Developers therefore optimise their products around Platform A.

More developers create products compatible with Platform A.

More users consequently find Platform A convenient.

This produces:

Users → Developers → Compatibility → More Users → Greater Design Familiarity → More Users

The design language therefore becomes a form of ecosystem lock-in.

17. Design Language and Switching Costs

Switching costs may be:

Financial

Users lose paid subscriptions or accumulated benefits.

Technical

Users must reinstall or reconfigure services.

Cognitive

Users must learn a different interface.

Data-related

Users must migrate data.

Social

Contacts and social networks remain within the incumbent system.

Behavioural

Users become accustomed to established interface patterns.

A dominant undertaking can therefore possess significant behavioural market power even where competitors remain technically available.

18. Design Language and Interoperability

Interoperability is particularly important.

Suppose a dominant operating system provides:

• biometric authentication;
• background processing;
• notifications;
• voice integration;
• payment APIs; and
• device-level permissions

to its own applications but provides competitors with inferior access.

The resulting competitive advantage may appear as a design difference, although its underlying cause is API or infrastructure control.

The DMA expressly addresses this structural issue by requiring certain gatekeepers to provide third parties with access to OS features available to the gatekeeper's own services.

19. Design Language and Algorithmic Ranking

Modern design is increasingly algorithmic.

A platform may dynamically determine:

• which seller appears first;
• which video is recommended;
• which search result receives a visual card;
• which advertisement appears prominently;
• which product receives a badge;
• which payment method is highlighted.

Consequently, design control and algorithmic control are increasingly inseparable.

The relevant competition issue becomes:

Who controls the algorithm determining what the consumer sees?

This creates a new category of potential market power:

visibility power.

20. Design Language and Self-Preferencing

Self-preferencing can take subtle forms.

The legal assessment must still distinguish legitimate product design from exclusionary conduct.

Not every superior interface is an antitrust problem.

21. Legitimate Design Versus Anticompetitive Design

A platform may legitimately design its interface according to:

• security;
• privacy;
• accessibility;
• simplicity;
• fraud prevention;
• performance;
• consumer comprehension;
• technical reliability; or
• product differentiation.

Therefore, competition authorities should not assume:

“Different design = unlawful discrimination.”

The critical questions are:

1. Is the undertaking dominant?
2. Does it control an important gateway?
3. Does the design disadvantage rivals?
4. Is the disadvantage substantial?
5. Is there a credible technical or consumer-protection justification?
6. Is the design proportionate?
7. Can competitors compete effectively despite the design?
8. Is equivalent functionality available to rivals?

22. Consumer Welfare and Design

Design can affect consumer welfare in both positive and negative ways.

Positive effects

Good design can:

• reduce search costs;
• simplify transactions;
• increase security;
• reduce fraud;
• improve accessibility;
• make products easier to use.

Negative effects

Strategic design can:

• increase switching costs;
• reduce transparency;
• suppress rival visibility;
• manipulate defaults;
• make cancellation difficult;
• impair comparison;
• reinforce lock-in.

Competition law therefore needs to distinguish efficient design innovation from strategic exclusion through design.

23. Evidentiary Issues

Design-based competition cases require evidence beyond conventional market-share data.

Important evidence may include:

Internal documents

• UX specifications;
• design briefs;
• product roadmaps;
• A/B testing results;
• internal emails;
• competitor analyses.

Behavioural data

• click-through rates;
• conversion rates;
• switching rates;
• abandonment rates;
• default-selection rates.

Technical evidence

• API access;
• interoperability restrictions;
• latency differences;
• functionality differences.

Consumer research

• user comprehension;
• choice-screen experiments;
• switching behaviour;
• default effects.

Economic analysis

Authorities can compare:

observed consumer behaviour

with:

behaviour under a counterfactual neutral interface.

24. The Counterfactual Interface

A particularly useful analytical technique is the counterfactual-interface test.

Ask:

What would competition look like if the dominant platform presented its own product and rival products through materially equivalent design conditions?

For example:

Actual interface

• incumbent: one click;
• rival: four clicks.

Counterfactual

• incumbent: one click;
• rival: one click.

If consumer switching changes dramatically, this provides evidence that interface architecture may be contributing to market power.

This should be supplemented by evidence concerning causation, costs, consumer preferences and legitimate product-design explanations.

25. Relationship with Article 102 TFEU

Under EU competition law, design-related conduct may potentially fall within Article 102 where a dominant undertaking uses its position to engage in exclusionary conduct.

Possible theories include:

• self-preferencing;
• tying;
• discriminatory access;
• refusal/interoperability restrictions;
• leveraging;
• exclusionary ranking;
• foreclosure through defaults; and
• raising rivals' costs.

The Google Android judgment demonstrates how several apparently separate ecosystem practices can be examined as components of a broader strategy.

26. Relationship with the DMA

The Digital Markets Act goes further in some respects because it establishes ex ante obligations for designated gatekeepers.

This is particularly significant for design because traditional abuse-of-dominance litigation can require lengthy analysis of:

• dominance;
• abuse;
• effects;
• foreclosure;
• causation.

The DMA can instead impose specific obligations concerning:

• choice;
• interoperability;
• steering;
• data access;
• defaults;
• ranking;
• ecosystem openness.

The European Commission's 2026 enforcement against Google concerning self-preferencing and steering demonstrates how interface and platform architecture can become directly relevant to gatekeeper regulation.

27. Relationship with UK Competition Law

In the UK, the concept is increasingly relevant to the Strategic Market Status regime under the Digital Markets, Competition and Consumers Act 2024.

Google's general-search designation and the CMA's subsequent work on user choice show that competition regulation can examine not merely whether alternative services exist, but how users are presented with those alternatives.

This creates a particularly important conceptual transition:

From market access → to user access → to effective user choice.

28. Key Legal Tests

A useful analytical framework is:

Test 1 — Gateway power

Does the undertaking control a commercially important digital gateway?

Test 2 — Design dependence

Do competitors depend upon the undertaking's interface, operating system or platform?

Test 3 — Differential treatment

Does the platform give its own service materially better design conditions?

Test 4 — Competitive significance

Does the difference affect discovery, conversion, switching or interoperability?

Test 5 — Foreclosure

Does the conduct materially impair rivals' ability to compete?

Test 6 — Justification

Is there a legitimate objective explaining the design difference?

Test 7 — Proportionality

Could the objective be achieved through a less exclusionary design?

29. Emerging Concept: Interface Market Power

The concept can ultimately be expressed as:

Interface market power is the ability of a firm controlling a commercially important digital interface to influence the competitive conditions under which users discover, evaluate, select and transact with alternative providers.

It differs from traditional market power because it operates through attention, defaults, visibility, friction and behavioural architecture.

The firm may not control the competitor's product.

It controls the path by which the consumer reaches the competitor.

That distinction is increasingly important in digital competition law.

30. Conclusion

Design language can become a form of market power when control over interface architecture enables a dominant undertaking to shape the competitive environment in which consumers encounter and choose rival products.

The most important mechanisms are:

1. visual prominence;
2. ranking and recommendation;
3. defaults;
4. navigation and click friction;
5. linguistic framing;
6. pre-installation;
7. interoperability;
8. API access;
9. self-preferencing; and
10. switching architecture.

The case law and regulatory developments involving Google Shopping, Google Android, Microsoft, Epic Games v Apple, Epic Games v Google, and FTC v Amazon, together with the European Commission's browser-choice and contemporary DMA enforcement work, demonstrate the broader movement toward recognising that digital competition can be affected by the architecture of choice itself.

The central legal distinction remains crucial:

Good design improves a product; strategic design control can alter the conditions under which competing products are able to compete.

Accordingly, future competition-law analysis is likely to treat interface design, choice architecture, defaults, ranking, interoperability and behavioural friction as economically significant components of market power, particularly where a dominant digital gateway controls access between businesses and users.