Log Sanitizer Without Uploading
Redact PII Before It Leaves Your Machine

Log sanitizer without uploading: the only safe way to redact PII from a log file is a tool that processes everything in your browser — because a sanitizer that uploads your log to a server to clean it has just sent the sensitive data you wanted to remove to a third party, which is exactly the problem you were trying to solve.

The Irony of Server-Side Log Sanitizers

Think about the sequence of events with a server-side sanitizer:

You've solved the problem downstream (the person you share the log with doesn't see the PII) while creating a larger problem upstream (a server you don't control now has a copy of everything you were trying to protect).

What Your Log Files Actually Contain

Developers often underestimate how much sensitive data accumulates in logs. A typical web application log will contain some or all of these:

Tool Comparison

Sanitize Logs Without Any Tool

For targeted one-off redaction on the command line:

# Redact email addresses
sed -E 's/[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/[EMAIL]/g' app.log

# Redact IPv4 addresses
sed -E 's/\b([0-9]{1,3}\.){3}[0-9]{1,3}\b/[IP]/g' app.log

# Redact Authorization header values (Bearer tokens, API keys)
sed -E 's/(Authorization: Bearer )[^\s]+/\1[TOKEN]/g' app.log

# Chain multiple patterns
cat app.log \
  | sed -E 's/[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/[EMAIL]/g' \
  | sed -E 's/\b([0-9]{1,3}\.){3}[0-9]{1,3}\b/[IP]/g' \
  | sed -E 's/(Authorization: Bearer )[^\s]+/\1[TOKEN]/g' \
  > app.redacted.log

Or in Python, which handles larger files more gracefully and gives you more control over patterns:

import re, sys

PATTERNS = [
    (re.compile(r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'), '[EMAIL]'),
    (re.compile(r'\b(?:\d{1,3}\.){3}\d{1,3}\b'),               '[IP]'),
    (re.compile(r'Bearer [A-Za-z0-9\-._~+/]+=*'),               'Bearer [TOKEN]'),
    (re.compile(r'[A-Za-z0-9\-_]{20,}\.[A-Za-z0-9\-_]+\.[A-Za-z0-9\-_]+'), '[JWT]'),
]

with open(sys.argv[1]) as f:
    for line in f:
        for pattern, replacement in PATTERNS:
            line = pattern.sub(replacement, line)
        print(line, end='')

How to Verify a Browser Tool Is Truly Client-Side

Compliance Context

For teams working under HIPAA or GDPR, the processing location matters legally — not just operationally: