First-party data: what it is and why it became a priority

Third-party cookies did not die. In April 2025 Google gave up on removing them from Chrome, and in October of the same year it retired Privacy Sandbox altogether, the set of technologies that was supposed to replace them. If you spent three years hearing that "the end of cookies" was coming, you might conclude the topic is closed.

That would be an expensive mistake. The signal companies get from outside keeps shrinking through other routes: Safari and Firefox block third-party cookies by default, iPhones ask permission before any app can track the user, ad blockers cut pixels off, and privacy laws such as Brazil’s LGPD or Europe’s GDPR require a legal basis for every use of personal data. That is why first-party data became a priority, cookie or no cookie.

First-party data is the information a company collects directly from its own customers and visitors, through channels it controls: website, app, online store, CRM, messaging, customer support and surveys. Because it does not depend on intermediaries, it is more accurate, cheaper over time and easier to use within privacy law than data bought from third parties.

First, second, third and zero-party data: what is the difference?

The classification is about who collected the data and what relationship they have with the customer. It is not about the type of information but about its origin. The same email address can be first-party (the customer signed up at your store) or third-party (it came from a purchased list).

Type	Who collects it	Example	Reliability
Zero-party	You, with the customer stating it on purpose	Preference quiz, survey answers, preferred size	High, but can go stale
First-party	You, through the customer’s interactions	Orders, site browsing, support history, CRM leads	High
Second-party	A partner that shares it with you	A marketplace’s or partner brand’s data, under agreement	Medium to high
Third-party	Companies with no relationship to the customer	Purchased audience segments, ad network cookies	Low and increasingly restricted

In practice, zero-party data is a subset of first-party data. The distinction matters because it changes what you can do: what the customer told you ("I prefer to be contacted on WhatsApp") carries more weight than what you inferred from behavior.

If cookies did not die, why did first-party data become a priority?

Because the problem was never just Chrome. Four forces are at work at the same time, and none of them has retreated.

1. The outside signal is already broken

Safari, which carries huge weight among iPhone users, has blocked third-party cookies by default for years. Apple’s App Tracking Transparency forces every app to ask for permission to track, and many people say no. Add ad blockers and cookies that expire within days, and your site’s pixel sees a shrinking slice of what actually happens. You already feel it when Ads Manager reports 80 sales and your ERP records 130.

2. Ad algorithms now run on the conversions you send them

Meta’s Advantage+ and Google’s Performance Max optimize based on the conversion events they receive. The more complete and reliable the data you send back (confirmed sale, real value, returning customer), the better they choose who sees the ad. That is first-party data feeding media server-side, not through a browser cookie. A study by Advertiser Perceptions in partnership with Google, surveying Brazilian advertisers between December 2024 and January 2025, shows how big the bet is: 91% of advertisers said they attribute their 2024 revenue growth directly to personalized ads, which accounted for 47% of their sales that year. Personalization without your own data gets shallower every year.

3. Privacy law favors whoever has a direct relationship with the customer

Data you collected yourself, with a clear purpose and a defined legal basis, is far easier to justify than a list of unknown origin. Buying third-party audiences transfers to you a risk you cannot audit.

4. AI without your own context is generic AI

Every competitor has access to the same AI models. What sets the answer apart is the context you give them: your orders, your margin per product, your returning customers. The asset is the data, not the model.

Google made the uncertainty plain, by the way: when it retired Privacy Sandbox in October 2025 citing low adoption, Chrome kept the cookie but lost any long-term plan. Building your measurement strategy on a mechanism that is already blocked in part of the browser market is a poor bet.

First-party data examples your company probably already has

Most mid-sized companies already collect plenty of their own data. The problem is that it lives in systems that do not talk to each other. Some common examples:

• Transactional: orders, items, value, payment method, coupon used, returns.
• Behavioral: pages viewed, products added to cart, GA4 events, email opens.
• Commercial: leads, funnel stage, loss reason and time to close, all in the CRM.
• Relationship: chat conversations, support tickets, NPS scores.
• Declared (zero-party): contact preferences, survey answers, sign-up details.

On its own, each one answers small questions. Together, they answer the ones that matter: which channel brings customers who buy again, which campaign attracts people who return products, what a lead from each source is really worth. It is the same problem we covered in data silos.

What is joining the data worth? A worked example

Picture an online cosmetics store with 12,000 customers last year and an average order value of BRL 180 (about USD 33). The numbers below are a simulation to illustrate the reasoning, not research.

• 8,400 customers (70%) bought only once: 8,400 orders, BRL 1,512,000.
• 3,600 customers (30%) bought more than once, averaging 3.2 orders each: 11,520 orders, BRL 2,073,600.

Total revenue: BRL 3,585,600. The 30% who come back account for 57.8% of revenue. Here is the point: Ads Manager does not know who is a repeat customer. It optimizes for "purchase", any purchase. Only by matching store orders to the source of each customer’s first order (email or tax ID as the key) do you find out that, say, customers from organic search buy again twice as often as those from an aggressive discount ad. That is a budget decision no third-party data will give you.

How to start collecting first-party data (without a six-month project)

1. Pick your identification key. Email, phone or a customer ID. Without a shared key across website, CRM and store, you collect data you cannot match. This decision comes before any tool.
2. Inventory what already exists. List each system, what data it holds and who has access. There is almost always more than it seems, just scattered.
3. Fix collection on your site. Well-defined GA4 events, standardized UTMs and server-side conversion tracking (Meta Conversions API, Google enhanced conversions). This recovers part of the signal the browser loses.
4. Give customers legitimate reasons to identify themselves. An account with real benefits (shipping, order history, loyalty points), a useful quiz, support that asks for the minimum. A fair trade, not a 14-field form.
5. Centralize and use it. Bring the sources into one queryable place, whether a data warehouse or a tool that already connects your systems. And define two or three business questions this data must answer in the first month.

Step 5 is where most companies stall. Collecting is the easy part. Data sitting in a CRM that nobody queries is worth nothing.

First-party data and privacy law: what changes in practice?

Having the data does not give you the right to use it any way you like. Laws like the LGPD and GDPR require a legal basis for each purpose (consent, contract performance, legitimate interest and others), transparency about use and collection limited to what is necessary. A few practical safeguards:

• A cookie banner that actually respects the choice, not a decorative notice.
• A privacy policy that says in plain language what the data is for.
• Sending data to ad platforms with hashed email and phone, as those platforms already require.
• A defined retention period: data kept forever is a liability, not an asset.

This is not legal advice. For specific cases, talk to whoever handles data protection at your company.

Where first-party data strategies usually fail

The most common mistake is not collecting too little. It is collecting without deciding what for. We see three recurring patterns:

Tool before question. The company buys an expensive CDP and, a year later, uses it to send birthday emails. Start with the decision you want to improve.

Dirty data at the source. A CRM with the same customer entered three times, free-text fields with no standard and lead source left blank. Matching that produces wrong numbers that look precise. Read up on data quality before promising any report.

Nobody owns the data. Marketing thinks it belongs to IT, IT thinks it belongs to sales. Without an owner, the identification key gets lost with the first new system that comes in.

Frequently asked questions

What is first-party data?

It is the data your company collects directly from customers and visitors through its own channels, such as website, app, store, CRM and support. It includes orders, browsing, leads and survey answers. It is considered the most reliable because it comes from a direct relationship.

What is the difference between first-party and third-party data?

First-party data is collected by you, from the customer. Third-party data is collected by companies with no relationship to the customer and sold or shared at scale, such as ad network audience segments. Third-party data is broader, but less accurate and increasingly limited by browsers and privacy laws.

Does first-party data require consent?

Not always. Privacy laws provide other legal bases, such as contract performance (using an address to deliver an order) and legitimate interest. Advertising cookies and targeted marketing, however, usually require consent. The key is having the right legal basis for each purpose.

What is zero-party data?

It is information the customer shares intentionally and explicitly: preferences, purchase intentions, quiz answers. Technically it is part of first-party data, but it carries more weight because it was declared, not inferred.

Are third-party cookies going away?

In Chrome, there is no date for it: Google dropped the removal in 2025. But Safari and Firefox already block them by default, and privacy restrictions keep growing. For planning purposes, treat third-party cookies as a partial and increasingly unreliable signal.

Your own data is the only data nobody can switch off

Third-party data depends on the goodwill of browsers, operating systems and regulators, and all three have shown they can change the rules from one quarter to the next. The data born from your relationship with the customer stays yours. The edge does not belong to whoever collects the most, but to whoever can ask that data questions and decide fast: which channel brings customers who come back, where margin disappears, which campaign deserves to scale. That is exactly what Sherlok does: it connects Meta Ads, Google Ads, GA4, your CRM and spreadsheets and lets you ask questions in plain language, getting the analysis ready-made. If your conversion attribution still depends only on what the pixel can see, the first step is bringing together what is already yours.