Grepture Proxy

An LLM API proxy that detects and redacts PII, blocks sensitive content, and tokenizes fields — all before requests reach your AI provider.

Quick Start

# Copy and edit the example rules
cp rules.example.json rules.json

# Start the proxy
bun run src/index.ts

The proxy starts on port 4001 by default. Send requests through it by setting the X-Grepture-Target header to your upstream API:

curl http://localhost:4001/proxy/ \
  -H "Authorization: Bearer any-token" \
  -H "X-Grepture-Target: https://api.anthropic.com/v1/messages" \
  -H "X-Grepture-Auth-Forward: Bearer sk-ant-..." \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5-20250514",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "My email is john@example.com"}]
  }'

The proxy will redact john@example.com before it reaches the API, based on your rules.

Configuration

Environment Variable	Required	Default	Description
GREPTURE_API_KEY	No	—	If set, only requests with this Bearer token are allowed. If unset, any token is accepted.
GREPTURE_RULES_FILE	No	rules.json	Path to rules configuration file
GREPTURE_PLUGINS	No	—	Comma-separated paths to plugin modules to load at startup
PORT	No	4001	Port to listen on

Rules

Rules are defined in a JSON file (default: rules.json). See rules.example.json for the full format.

Each rule has:

• conditions — when to apply (match on headers, body, URL, model)
• actions — what to do (redact PII, find/replace, tokenize, block, log)
• apply_to — input (before forwarding), output (on response), or both
• sampling_rate — percentage of requests to apply to (1-100)

Available Actions

Action	Description
redact_pii	Detect and redact PII using regex patterns (email, phone, SSN, credit card, IP, address, DOB)
find_replace	Find and replace text (literal or regex)
tokenize	Replace JSON fields with tokens, store originals for later restoration
redact_field	Replace specific JSON fields with a fixed value
block_request	Block the request with a custom status code and message
log_only	Tag the request for logging without modifying it

Rules are reloaded automatically when the file changes, or on SIGHUP.

Docker

docker build -t grepture-proxy .

docker run -p 4001:4001 \
  -v $(pwd)/rules.json:/app/rules.json \
  grepture-proxy

How It Works

Client → Proxy → [Auth] → [Input Rules] → [Forward] → [Output Rules] → [Detokenize] → Client

1. Authenticate the request (optionally validate API key if GREPTURE_API_KEY is set)
2. Apply input rules (redact PII, block, tokenize)
3. Forward to the upstream API (set via X-Grepture-Target)
4. Apply output rules to the response
5. Restore tokenized values
6. Return the response

Supports both buffered and streaming (SSE) responses. Token restoration works across streamed chunks.