Browsers, and the browser engines that power them, provide critical public infrastructure to over five billion people. To cover the high cost of maintaining such complex feats of engineering, browser vendors and search engine providers have improvised a system in which money is levied from search revenue and distributed to browsers. Over the years, this ad hoc system has succeeded in providing some funding to browsers but it suffers from a muddled lack of transparency and has known detrimental effects on funding attribution, concentration, search quality, privacy, misinformation, publisher revenue, and opinion pluralism. This specification captures the web community's experience with the current system so as to refine requirements and formalizes a browser/search levy that improves on the current one and addresses its shortcomings.


As of 2022, 63% of the world population, or roughly 5 billion people, used the Internet ([[?Internet-Users]]). While some of these may not use a browser (the application used to navigate the web) regularly, all use a browser engine (the software component that both browsers and other apps use to render web content) regularly as those are widely used in applications in addition to forming the core of [=browsers=].

[=Browsers=] and [=browser engines=] are provided to people free of charge, as public goods. Their continued provision is critical since without them the web collapses. They are also complex: for instance, in 2022 Chromium (the [=browser engine=] powering Google Chrome and other [=browsers=]) ran to about 35 million lines of code. The total annual cost of maintaining the three primary browser engines is estimated to be around $2 billion USD ([[?Where-Browsers]]). While this cost is significant, it is only a small fraction of the direct value (monetary or otherwise) produced by the web.

In order to assemble the funds required to operate, almost all browser vendors rely on variations on the same strategy: they exercise an ad hoc levy on search engine revenue. Variations on this levy include selling the search engine [=default=] (the initial and typical approach), [=royalties=] on search volume, or [=intra-company transfers=] (when the search engine and browser belong to the same company). Taken together, these strategies form the [=AHLD=] system, which is described further in the next section.

Despite its critical importance to web infrastructure, the [=AHLD=] system is opaque and poorly documented, and suffers from a number of undesirable shortcomings that have large-scale detrimental effects on the web. By formalizing this levy and deliberately architecting it to produce improved results, we can simultaneously put the funding of critical public digital infrastructure on much surer footing and address the [=AHLD=] system's issues.

The Ad Hoc Levy on Defaults (AHLD) System

The Ad Hoc Levy on Defaults (AHLD) is a system in which a portion of search engine revenue is levied and used to pay browsers. (It is also used for operating systems and other agents, but our focus in this document is browsers.) The levy ensures that browsers, which constitute criticial infrastructure for the web, are provided free of charge to people. It can take multiple typical forms:

These deals are negotiated bilaterally, and in practice an [=AHLD=] agreement between a browser vendor and a search engine vendor can marry aspects from several of these forms.

[=AHLD=] levies are economically significant and constitute one of the larger commercial exchanges on the web. For instance, in the year 2021 Google Search spent over $26 billion USD on [=default placement=] deals ([[?26-Billion-Default]]) — which does not include its [=intra-company transfer=] costs — and paid 36% of its search advertising revenue made in Safari to Apple ([[?Apple-36]]). In 2020, Mozilla made 86% of its revenue from the Google Search levy ([[?Mozilla-Revenue]]). Note: We have to use relatively old numbers due to the unfortunate lack of transparency that the [=AHLD=] system suffers from. To the best of our knowledge, the situation has not significantly evolved since.

Reviewing the AHLD

The [=AHLD=] levy was an excellent invention and remains a great idea twenty years on. Taking a system view of the web, search is indeed one of the logical places at which to apply a levy. Search extracts value from content and behavior on the web (it would have no value otherwise) and renders it available at a functional choke point (it is one of the required components of web discovery). In turn, the value of web content is only possible because browsers provide critical infrastructure services that render that content available and attractive to people, and for the most part safe. In an idealized view, we can envision a virtuous, regenerative cycle: the search levy finances core web infrastructure and that core web infrastructure makes the web successful such that search engines enjoy strong businesses that can be levied from.

Unfortunately, the [=AHLD=] levy has failed to evolve as the web grew from a time of relative infancy when only 14% of the world population (fewer than a billion, [[?Internet-Users]]) used the Internet to the essential part of society that it is today. Over time, serious shortcomings with this ad hoc approach have surfaced that have not been addressed. It is incumbent on the web community to step up and hammer out an agreement for a better levy, as well as to commit to maintaining it so as to avoid the accumulation of problems ([[rfc9413]]). The changes need not be revolutionary since the core principle — a levy on search to pay for web infrastructure — can readily remain the same. However, as pressure mounts to address the problems caused by an unmaintained, ad hoc system, if we fail to act we may lose the levy altogether. Should that happen, the web will suffer from the impact on its infrastructure and we may find it very difficult to maintain a high-quality browser engine, let alone a diverse set of them.

The rest of this section captures the shortcomings of the [=AHLD=] levy.

Search is a key architectural component of the web, browsers provide critical infrastructure, but unfortunately there is no transparency into the system. Almost everything that the web community knows about [=AHLD=] we know thanks to material released via court cases. If we are to take seriously the W3C's goals of building a web for all humankind, we need to ensure that the web community is able to evaluate how the beating heart of web infrastructure operates.

There is also no accountability concerning the bilateral ad hoc deals made within [=AHLD=]. A search engine may impose additional requirements on browser vendors that might not be in users' best interests (e.g. that the browser must not implement certain privacy protections) without oversight. A system deployed at such a scale needs to be trustworthy.

It does not respect the priority of constituencies ([[?ethical-web-principles]]). Search deals made via the levy can have terms that forbid the browser from intervening on the search engine results page (SERP) even when such changes would be beneficial to the user. For instance, a search engine may benefit from making its ads look like search results or from pushing users to be logged in, sacrificing privacy. A browser is expected to counteract such practices, but the [=AHLD=] levy prevents that.

The system gives power to search engines over how browsers work, including over aspects of browsers that may not seem search-related, for instance privacy features that can be used for advertising attribution may have to be approved by the search engine before they can ship in a browser. The lack of public accountability over the royalties part of the system means that there is a strong information asymmetry between the search engine and the browser in terms of where the royalties come from and what may affect them, which empowers the search engine to threaten potential revenue loss when the browser makes a change they dislike in ways that cannot be verified. Because of this, the search engine is both judge and party in the relationship, and in a position to exert undue influence over browsers.

Browsers are paid by the [=AHLD=] levy and may be subject to private requirements imposed by search engines, but from the perspective of the web community no requirements are placed on browsers in exchange for benefitting from the system.

The levy system pays for browsers but it does not pay for browser engines. [=Browser engines=] are the more complicated component and ought to be supported directly. As things stand, a [=browser=] can use an open source [=browser engine=], collect funds from the levy, but not contribute anything back to the browser engine. This free riding is detrimental to the maintenance of a rich ecosystem of browser engines.

Worryingly, most appropriated funds don't go towards web infrastructure. While the purpose of the levy is manifestly to support web infrastructure, the overwhelming majority of funds is directed elsewhere. To take but one example: based on 2021 numbers, of the $26 billion USD that Google Search paid in levy, $18 billion went to Apple (about 70%). There is scant evidence that Apple, a publicly-traded company, spends in the vicinity of $18 billion USD per year on web infrastructure. The levy therefore suffers from very low efficiency, and in turn this causes value produced on the web to be directed outside of the web, which subsidizes its proprietary competitors.

The logic of applying a web infrastructure levy on search is because search can be considered to distill the value produced by publishers, ecommerce sites, and content creators. Unfortunately, publishers, ecommerce sites, and content creators have no say in a system eventually build on their work. While indexing content for the purpose of providing links back to the original source is evidently in everyone's interest, the lack of checks and balances in the system has led to a race to the bottom in which search engines provide fewer-and-fewer links back to sources ([[?AMP]]) while increasing the number of non-linking purposes for which they process the indexed content, such as generative AI.

Last but not least, the manner in which the [=AHLD=] system is structured means that it mechanically increases concentration in the search market. Few people change their default search engine (particularly on mobile devices), which means that purchasing a [=default placement=] effectively purchases market share. In turn, the search engine with the highest market share has greater profits from which to pay a higher price for further [=default placements=]. This eventually leads to almost every browser defaulting to the same search engine, and that search engine dominating the web by insuperable margins. In turn, this artificially-crated and -sustained concentration creates further problems:

While it is necessary to take stock of the [=AHLD=]'s shortcomings, and while having left it to linger too long in outdated ad hoc arrangements has caused these shortcomings to fester, these problems, once identified, can be addressed. The web community has a responsibility to do so quickly and effectively, as well as durably.

Requirements for a Web Infrastructure Search Endowment (WISE)


Operational Outline of the Web Fund


Notes on Choice Dialogs

tk simply show how they fail to meet requirements at a satisfactory level lots of testimony from Apple and Mozilla (cite transcripts) that they aren't user-friendly


The following people (in alphabetical order) have provided invaluable input into this draft: Dietrich Ayala, Matthew Frehlich, and Max Gendler.