Phileas 1.0.0

Phileas (.NET)

A .NET port of Phileas (Java) — a library to deidentify and redact PII, PHI, and other sensitive information from text.

• Check out the documentation or details and code examples.
• Built by Philterd.
• Commercial support and consulting is available - contact us.

Overview

Phileas (.NET) is a library for detecting and redacting Personally Identifiable Information (PII) from text. Define a policy that describes which types of sensitive data to find, choose how each type should be handled, and call a single method to get back redacted text.

Phileas analyzes text searching for sensitive information such as email addresses, phone numbers, SSNs, credit card numbers, and many other types of PII/PHI. When sensitive information is identified, Phileas can manipulate it in a variety of ways: the information can be redacted, masked, hashed, or replaced with a static value. The user defines how to handle each type of sensitive information through policies (YAML or JSON).

Other capabilities include referential integrity for redactions, conditional logic for redactions, and a CLI.

Phileas requires no external dependencies (e.g. no ChatGPT/etc.) and is intended to be lightweight and easy to use.

Supported Filter Types

Installation

Add the NuGet package to your project:

dotnet add package Phileas

Quick Start

Redact an email address

using Phileas.Policy;
using Phileas.Policy.Filters;
using Phileas.Services;
using PhileasPolicy = Phileas.Policy.Policy;

var policy = new PhileasPolicy
{
    Name = "my-policy",
    Identifiers = new Identifiers
    {
        EmailAddress = new EmailAddress()
    }
};

var result = new FilterService().Filter(
    policy: policy,
    context: "default",
    piece: 0,
    input: "Contact john.doe@example.com for help."
);

Console.WriteLine(result.FilteredText);
// Output: Contact {{{REDACTED-email-address}}} for help.

Redact multiple PII types at once

var policy = new PhileasPolicy
{
    Name = "full-redaction",
    Identifiers = new Identifiers
    {
        EmailAddress = new EmailAddress(),
        PhoneNumber  = new PhoneNumber(),
        Ssn          = new Ssn(),
        CreditCard   = new CreditCard(),
        ZipCode      = new ZipCode()
    }
};

var result = new FilterService().Filter(
    policy: policy,
    context: "default",
    piece: 0,
    input: "Call 555-867-5309 or email jane@example.com. SSN: 123-45-6789."
);

Console.WriteLine(result.FilteredText);

Redact terms from a custom dictionary

The Dictionary filter matches a list of terms you supply and optionally uses fuzzy (approximate) matching.

using Phileas.Policy;
using Phileas.Policy.Filters;
using Phileas.Services;
using PhileasPolicy = Phileas.Policy.Policy;

var policy = new PhileasPolicy
{
    Name = "dictionary-policy",
    Identifiers = new Identifiers
    {
        Dictionaries = new List<Dictionary>
        {
            new Dictionary
            {
                Name  = "project-names",
                Terms = new List<string> { "Project Phoenix", "Operation Nightfall" },
                Fuzzy = false
            }
        }
    }
};

var result = new FilterService().Filter(
    policy: policy,
    context: "default",
    piece: 0,
    input: "The memo referenced Project Phoenix and Operation Nightfall."
);

Console.WriteLine(result.FilteredText);
// Output: The memo referenced {{{REDACTED-dictionary}}} and {{{REDACTED-dictionary}}}.

Detect named entities with PhEye

The PhEye filter delegates entity recognition to a remote PhEye NLP service and redacts the entities it finds.

using Phileas.Policy;
using Phileas.Policy.Filters;
using Phileas.Services;
using PhileasPolicy = Phileas.Policy.Policy;

var policy = new PhileasPolicy
{
    Name = "pheye-policy",
    Identifiers = new Identifiers
    {
        PhEyes = new List<PhEye>
        {
            new PhEye
            {
                PhEyeConfiguration = new PhEyeConfiguration
                {
                    Endpoint = "http://localhost:8080",
                    Labels   = new List<string> { "Person" }
                }
            }
        }
    }
};

var result = new FilterService().Filter(
    policy: policy,
    context: "default",
    piece: 0,
    input: "John Smith joined the meeting."
);

Console.WriteLine(result.FilteredText);
// Output: {{{REDACTED-person}}} joined the meeting.

Inspect detected spans

Every result includes a list of Span objects that describe what was found:

foreach (var span in result.Spans)
{
    Console.WriteLine($"[{span.FilterType}] '{span.Text}' at {span.CharacterStart}-{span.CharacterEnd} → '{span.Replacement}'");
}

Filter Strategies

The default strategy is REDACT, which replaces PII with a formatted token such as {{{REDACTED-email-address}}}. You can customise the strategy on each filter:

using Phileas.Filters;
using Phileas.Policy.Filters.Strategies;

// Mask the last 4 characters and hide the rest with '*'
var ssnStrategy = new SsnFilterStrategy
{
    Strategy = AbstractFilterStrategy.Last4
};

var policy = new PhileasPolicy
{
    Name = "mask-policy",
    Identifiers = new Identifiers
    {
        Ssn = new Ssn { Strategies = new List<SsnFilterStrategy> { ssnStrategy } }
    }
};

Redaction Strategies

Static replacement example

var emailStrategy = new EmailAddressFilterStrategy
{
    Strategy        = AbstractFilterStrategy.StaticReplace,
    StaticReplacement = "user@redacted.invalid"
};

Context Service and Referential Integrity

When using RANDOM_REPLACE, the Context Service ensures the same PII token always maps to the same replacement value within a named context. This preserves referential integrity across documents that reference the same identity.

// FilterService uses InMemoryContextService automatically,
// but you can supply your own implementation.
IContextService contextService = new InMemoryContextService();

var result = new FilterService().Filter(
    policy: policy,
    context: "patient-123",   // all calls sharing this name reuse the same mappings
    piece: 0,
    input: "SSN: 123-45-6789",
    contextService: contextService
);

To share replacement values across processes or persist them between runs, implement IContextService:

public class RedisContextService : IContextService
{
    private readonly IDatabase _db;

    public RedisContextService(IDatabase redisDatabase) => _db = redisDatabase;

    public string? Get(string contextName, string token)
    {
        var value = _db.HashGet(contextName, token);
        return value.IsNull ? null : (string?)value;
    }

    public void Put(string contextName, string token, string replacement)
        => _db.HashSet(contextName, token, replacement);
}

See docs/context-service.md for a full walkthrough.

Building and Testing

dotnet build Phileas.slnx
dotnet test  Phileas.slnx

License

Copyright 2026 Philterd, LLC.

Licensed under the Apache License, Version 2.0. See LICENSE for details.

"Phileas" and "Philter" are registered trademarks of Philterd, LLC.

This project is a .NET port of Phileas, which is also Apache-2.0 licensed.