> For the complete documentation index, see [llms.txt](https://docs.raga.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.raga.ai/ragaai-catalyst/concepts/uploading-data/trace-masking-functions.md).

# Trace Masking Functions

While RagaAI Catalyst sits on-prem for complete data security, enterprises might want to redact certain information, keywords, or patterns from their traces logged on the system. This can be done using custom Python functions as follows:

* **Prerequisites**

  Users need to define the relevant platform keys and Tracer object as usual:

```python
from ragaai_catalyst.tracers import Tracer
from ragaai_catalyst import (
    RagaAICatalyst,
    init_tracing
)

# Initialize RagaAI Catalyst
catalyst = RagaAICatalyst(
    access_key="<your-access-key>",
    secret_key="<your-secret-key>",
    base_url="https://catalyst.raga.ai/api"
)

# Setup tracing
tracer = Tracer(
    project_name="<your-project-name>",
    dataset_name="<your-dataset-name>",
    tracer_type="langchain"
)
```

* **Defining Custom Masking Functions**

  Users can define their custom Python logic to replace certain keywords with a redaction phrase as shown below:

```python
def masking_function(value):
    # Mask specific medical symptoms
    symptoms = ['Fever', 'Cough', 'Headache']
    for symptom in symptoms:
        # Case insensitive replacement using regex
        value = re.sub(rf'\b{symptom}\b', '<REDACTED SYMPTOM>', value, flags=re.IGNORECASE)

    return value

# Another sample masking function
def another_masking_function(value):
    """
    Returns masked strings with dates and emails redacted
    """
    # Mask dates in various formats (YYYY-MM-DD, MM/DD/YYYY, etc.)
    value = re.sub(r'\b\d{4}-\d{2}-\d{2}\b', '<REDACTED DATE>', value)
    value = re.sub(r'\b\d{1,2}/\d{1,2}/\d{4}\b', '<REDACTED DATE>', value)
    value = re.sub(r'\b[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}\b', '< REDACTED EMAIL ADDRESS>', value)
    return value
```

* **Enabling Masking Function**

  Lastly, users can pass the desired masking function (limited to one) to the initialized Tracer object using the `register_masking_function` method as follows:

```python
tracer.register_masking_function(masking_function)
init_tracing(catalyst=catalyst, tracer=tracer)
```

* **Running Your Application**

  Your RAG application can be defined further as usual. Any LLM calls should be traced with the above masking logic applied.


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