Pseudonymisation or anonymisation – what's the difference, and what does GDPR require?
Short answer
Pseudonymisation replaces names and other identifiers with codes, while the key is kept separately. The data is still personal data for whoever holds the key. Anonymisation removes any way of identifying the person at all – and anonymous data falls outside GDPR. True anonymisation is hard, especially with free text. Pseudonymisation, on the other hand, is named in GDPR as an important safeguard, and in 2025 the Court of Justice of the EU (Case C-413/23 P) confirmed that whether data is personal data for a recipient depends on whether that recipient can realistically identify the people.
Try it yourself
Type some text and see it pseudonymised. The text never leaves your browser.
Pseudonymisation across a whole dataset
| Customer | Location | Topic | |
|---|---|---|---|
| Sarah Murphy | sarah.murphy@example.com | Cork | Refund |
| Daniel Kelly | daniel.kelly@example.com | Galway | Delivery |
| Claire Walsh | claire.walsh@example.com | Limerick | Complaint |
| Thomas Camilleri | thomas.camilleri@example.com | Sliema | Delivery |
| Emma Byrne | emma.byrne@example.com | Dublin | Refund |
Enquiry Hi, my name is Sarah Murphy and I returned order 7012345678 two weeks ago, but I still haven't received my money. Please transfer it to IE29 AIBK 9311 5212 3456 78. Kind regards, Sarah
| Customer | Location | Topic | |
|---|---|---|---|
| [PERSON_1] | [EMAIL_1] | [STED] | Refund |
| [PERSON_2] | [EMAIL_2] | [STED] | Delivery |
| [PERSON_3] | [EMAIL_3] | [STED] | Complaint |
| [PERSON_4] | [EMAIL_4] | [STED] | Delivery |
| [PERSON_5] | [EMAIL_5] | [STED] | Refund |
Enquiry Hi, my name is [PERSON_1] and I returned order [ID_1] two weeks ago, but I still haven't received my money. Please transfer it to [IBAN_1]. Kind regards, [PERSON_1]
Sarah Murphy and Emma Byrne are waiting for a refund and should get a reply today. Thomas Camilleri has waited 10 days for a parcel. Suggested reply to Sarah Murphy: "Dear Sarah Murphy, thank you for your patience. Your money is on its way and will be in your account within 5 working days."
[PERSON_1] and [PERSON_5] are waiting for a refund and should get a reply today. [PERSON_4] has waited 10 days for a parcel. Suggested reply to [PERSON_1]: "Dear [PERSON_1], thank you for your patience. Your money is on its way and will be in your account within 5 working days."
| Candidate | Born | ID number | Employer | Experience |
|---|---|---|---|---|
| Louise Brennan | 1985-03-12 | 1234567TA | Shannon Timber Ltd | 12 |
| Michael Doyle | 1992-11-02 | 2345678KB | Liffey Logistics Ltd | 4 |
| Maria Borg | 1988-06-21 | 0123488M | Grand Harbour Metals Ltd | 9 |
| David Fenech | 1979-01-30 | 0456779M | Valletta Pharma Ltd | 18 |
CV Louise Brennan has 12 years' experience in budgeting and monthly reporting at Shannon Timber Ltd. She implemented a new ERP system and leads a team of three. Contact: louise.brennan@example.com.
| Candidate | Born | ID number | Employer | Experience |
|---|---|---|---|---|
| [PERSON_1] | 40–49 years | [ID_1] | [VIRKSOMHED_1] | 12 |
| [PERSON_2] | 30–39 years | [ID_2] | [VIRKSOMHED_2] | 4 |
| [PERSON_3] | 30–39 years | [ID_3] | [VIRKSOMHED_3] | 9 |
| [PERSON_4] | 40–49 years | [ID_4] | [VIRKSOMHED_4] | 18 |
CV [PERSON_1] has 12 years' experience in budgeting and monthly reporting at [VIRKSOMHED_1]. The person implemented a new ERP system and leads a team of three. Contact: [EMAIL_1].
Louise Brennan and Maria Borg have more than 5 years' experience and should be invited to interview; ask Maria Borg about experience with ERP systems. Michael Doyle has 4 years' experience; the requirement is 5. A person makes the decision.
[PERSON_1] and [PERSON_3] have more than 5 years' experience and should be invited to interview; ask [PERSON_3] about experience with ERP systems. [PERSON_2] has 4 years' experience; the requirement is 5. A person makes the decision.
| Supplier | Contact | Account | Expires |
|---|---|---|---|
| Atlantic Components Ltd | Peter Walsh | IE64 IRCE 9205 0112 3456 78 | 2027-01-31 |
| Malta Data Hosting Ltd | Anna Grech | MT84 MALT 0110 0001 2345 MTLC AST0 01S | 2026-12-31 |
| Midlands Precision Ltd | Simon Nolan | IE12 BOFI 9000 0112 3456 78 | 2028-06-30 |
| Celtic Packaging Ltd | Nicole Ryan | IE02 AIBK 9310 6512 9876 54 | 2027-03-31 |
Terms Atlantic Components supplies specialist components for Project Skellig. The price is adjusted annually by the consumer price index plus 3%. Liability is capped at 10% of the annual contract value. Contact Peter Walsh about any changes.
| Supplier | Contact | Account | Expires |
|---|---|---|---|
| [VIRKSOMHED_1] | [PERSON_1] | [IBAN_1] | 2027-01-31 |
| [VIRKSOMHED_2] | [PERSON_2] | [IBAN_2] | 2026-12-31 |
| [VIRKSOMHED_3] | [PERSON_3] | [IBAN_3] | 2028-06-30 |
| [VIRKSOMHED_4] | [PERSON_4] | [IBAN_4] | 2027-03-31 |
Terms [VIRKSOMHED_1] supplies specialist components for [PROJEKT_1]. The price is adjusted annually by the consumer price index plus 3%. Liability is capped at 10% of the annual contract value. Contact [PERSON_1] about any changes.
Atlantic Components Ltd renews automatically unless it is terminated by 31 October. It is important for an internal project, so renegotiate the price rather than terminate. Celtic Packaging Ltd also renews automatically; the deadline is 31 December.
[VIRKSOMHED_1] renews automatically unless it is terminated by 31 October. It is important for an internal project, so renegotiate the price rather than terminate. [VIRKSOMHED_4] also renews automatically; the deadline is 31 December.
Fictional data. Point to a name or a pseudonym to see what belongs together.
Why not just anonymise?
Because you need to use the answer. When the AI suggests that [PERSON_2] should get a reply today, you need to know who that is. With pseudonymisation, the name is put back in on your side – with anonymisation, the link is gone for good.
What to do
- Find the identifiers.Names, emails, phone numbers, ID numbers, account numbers, addresses.
- Replace them with fixed codes.The same person gets the same code throughout the dataset.
- Watch out for free text.Names and numbers hide in messages and CVs.
- Generalise anything that could identify someone.A date of birth becomes an age group, a town becomes a region.
- Keep the key separate.The key must never be sent to the AI.
What the law says
- Article 4(5) GDPR – pseudonymisation
- The definition: data that can no longer be attributed to a person without additional information, which is kept separately.
- Recital 26 GDPR
- Pseudonymised data is personal data; anonymous data is not.
- Articles 25 and 32 GDPR
- Pseudonymisation is named as an appropriate measure.
- Court of Justice of the EU, Case C-413/23 P (EDPS v SRB), 4 September 2025
- Whether pseudonymised data is personal data for the recipient depends on the recipient's realistic means of identifying the people.
Questions and answers
Is data anonymous once the name is removed?
Rarely. Age, place of residence, job and free text can often give the person away. These are called quasi-identifiers.
Is pseudonymised data personal data for the AI provider?
It may or may not be, depending on the provider's realistic means of identifying the people. For you, holding the key, it is always personal data.
What does GoalCube do with free text?
GoalCube finds names, emails, phone numbers, addresses, ID numbers from EU countries and account numbers in free text, hides your secret words and writes gender neutrally.
Sources
Written by The GoalCube editorial team. Last updated 11 October 2026. GoalCube helps you follow the EU AI Act and GDPR. It is not legal advice.
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