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Presidio Anonymizer

The Presidio anonymizer is a Python based module for anonymizing detected PII text entities with desired values. Presidio anonymizer supports both anonymization and deanonymization by applying different operators. Operators are built-in text manipulation classes which can be easily extended.

Anonymizer Design

The Presidio-Anonymizer package contains both Anonymizers and Deanonymizers.

  • Anonymizers are used to replace a PII entity text with some other value by applying a certain operator (e.g. replace, mask, redact, encrypt)
  • Deanonymizers are used to revert the anonymization operation. (e.g. to decrypt an encrypted text).


see Installing Presidio.

Getting started

Simple example:

from presidio_anonymizer import AnonymizerEngine
from presidio_anonymizer.entities import RecognizerResult, OperatorConfig

# Initialize the engine:
engine = AnonymizerEngine()

# Invoke the anonymize function with the text, 
# analyzer results (potentially coming from presidio-analyzer) and
# Operators to get the anonymization output:
result = engine.anonymize(
    text="My name is Bond, James Bond",
        RecognizerResult(entity_type="PERSON", start=11, end=15, score=0.8),
        RecognizerResult(entity_type="PERSON", start=17, end=27, score=0.8),
    operators={"PERSON": OperatorConfig("replace", {"new_value": "BIP"})},


This example takes the output of the AnonymizerEngine containing an encrypted PII entity, and decrypts it back to the original text:

from presidio_anonymizer import DeanonymizeEngine
from presidio_anonymizer.entities import OperatorResult, OperatorConfig

# Initialize the engine:
engine = DeanonymizeEngine()

# Invoke the deanonymize function with the text, anonymizer results and
# Operators to define the deanonymization type.
result = engine.deanonymize(
    text="My name is S184CMt9Drj7QaKQ21JTrpYzghnboTF9pn/neN8JME0=",
        OperatorResult(start=11, end=55, entity_type="PERSON"),
    operators={"DEFAULT": OperatorConfig("decrypt", {"key": "WmZq4t7w!z%C&F)J"})},


You can run presidio anonymizer as an http server using either python runtime or using a docker container.

Using docker container

cd presidio-anonymizer
docker run -p 5001:3000 presidio-anonymizer 

Using python runtime


This requires the Presidio Github repository to be cloned.

cd presidio-anonymizer


curl -XPOST http://localhost:3000/anonymize -H "Content-Type: application/json" -d @payload

payload example:
"text": "hello world, my name is Jane Doe. My number is: 034453334",
"anonymizers": {
        "type": "mask",
        "masking_char": "*",
        "chars_to_mask": 4,
        "from_end": true
"analyzer_results": [
        "start": 24,
        "end": 32,
        "score": 0.8,
        "entity_type": "NAME"
        "start": 24,
        "end": 28,
        "score": 0.8,
        "entity_type": "FIRST_NAME"
        "start": 29,
        "end": 32,
        "score": 0.6,
        "entity_type": "LAST_NAME"
        "start": 48,
        "end": 57,
        "score": 0.95,
        "entity_type": "PHONE_NUMBER"


curl -XPOST http://localhost:3000/deanonymize -H "Content-Type: application/json" -d @payload

payload example:
"text": "My name is S184CMt9Drj7QaKQ21JTrpYzghnboTF9pn/neN8JME0=",
"deanonymizers": {
    "PERSON": {
        "type": "decrypt",
        "key": "WmZq4t7w!z%C&F)J"
"anonymizer_results": [
        "start": 11,
        "end": 55,
        "entity_type": "PERSON"

Built-in operators

Operator type Operator name Description Parameters
Anonymize replace Replace the PII with desired value new_value: replaces existing text with the given value.
If new_value is not supplied or empty, default behavior will be: <entity_type> e.g: <PHONE_NUMBER>
Anonymize redact Remove the PII completely from text None
Anonymize hash Hashes the PII text hash_type: sets the type of hashing. Can be either sha256, sha512 or md5.
The default hash type is sha256.
Anonymize mask Replace the PII with a given character chars_to_mask: the amount of characters out of the PII that should be replaced.
masking_char: the character to be replaced with.
from_end: Whether to mask the PII from it's end.
Anonymize encrypt Encrypt the PII using a given key key: a cryptographic key used for the encryption.
Anonymize custom Replace the PII with the result of the function executed on the PII lambda: lambda to execute on the PII data. The lambda return type must be a string.
Anonymize keep Preserver the PII unmodified None
Deanonymize decrypt Decrypt the encrypted PII in the text using the encryption key key: a cryptographic key used for the encryption is also used for the decryption.


When performing anonymization, if anonymizers map is empty or "DEFAULT" key is not stated, the default anonymization operator is "replace" for all entities. The replacing value will be the entity type e.g.: <PHONE_NUMBER>

Handling overlaps between entities

As the input text could potentially have overlapping PII entities, there are different anonymization scenarios:

  • No overlap (single PII): When there is no overlap in spans of entities, Presidio Anonymizer uses a given or default anonymization operator to anonymize and replace the PII text entity.
  • Full overlap of PII entitie spans: When entities have overlapping substrings,
    the PII with the higher score will be taken. Between PIIs with identical scores, the selection is arbitrary.
  • One PII is contained in another: Presidio Anonymizer will use the PII with the larger text even if it's score is lower.
  • Partial intersection: Presidio Anonymizer will anonymize each individually and will return a concatenation of the anonymized text. For example: For the text

    I'm George Washington Square Park.

    Assuming one entity is George Washington and the other is Washington State Park and assuming we're using the default anonymizer, the result would be:


Additional examples for overlapping PII scenarios


My name is Inigo Montoya. You Killed my Father. Prepare to die. BTW my number is:


  • No overlaps: Assuming only Inigo is recognized as NAME:

    My name is <NAME> Montoya. You Killed my Father. Prepare to die. BTW my number is:
  • Full overlap: Assuming the number is recognized as PHONE_NUMBER with score of 0.7 and as SSN with score of 0.6, the higher score would count:

    My name is Inigo Montoya. You Killed my Father. Prepare to die. BTW my number is: <
  • One PII is contained is another: Assuming Inigo is recognized as FIRST_NAME and Inigo Montoya was recognized as NAME, the larger one will be used:

    My name is <NAME>. You Killed my Father. Prepare to die. BTW my number is: 03-232323.
  • Partial intersection: Assuming the number 03-2323 is recognized as a PHONE_NUMBER but 232323 is recognized as SSN:

    My name is Inigo Montoya. You Killed my Father. Prepare to die. BTW my number is: <

Creating a new operator

Presidio anonymizer can be easily extended to support additional operators. See this tutorial on adding new operators for more information.

API reference

Follow the API Spec for the Anonymizer REST API reference details and Anonymizer Python API for Python API reference.