---
slug: "codingcoffee-pi-privacy-filter"
source_type: "readme"
source_url: "https://cdn.jsdelivr.net/gh/codingcoffee/pi-privacy-filter@main/README.md"
repo: "https://github.com/codingcoffee/pi-privacy-filter"
source_file: "README.md"
branch: "main"
---
# pi-privacy-filter

A [pi](https://pi.dev) extension that runs every prompt through a local privacy classifier (`openai/privacy-filter` via `@huggingface/transformers`) **before** it is sent to the LLM, and transparently **restores** the original values in the LLM's response.

```
user input ──► [redact] ──► LLM
                  │
                  └── placeholder→original mapping (in memory)

LLM response ──► [unredact via mapping] ──► you see the real values
```

Example:

- you type:    `My AWS account number is 22922829292`
- LLM sees:    `My AWS account number is [ACCOUNT_NUMBER_1]`
- you see:     `... My AWS account number is 22922829292 ...` (assistant's reply, restored)

The mapping lives in memory for the session only — nothing is written to disk by this extension. Your original message is still stored in the session file (since that's where pi keeps it); only the bytes leaving for the model are redacted.

## How it works

- Hooks the `context` event to mutate the deep-cloned messages pi is about to send to the model. User messages and tool results have their text run through the classifier; matched spans are replaced with stable placeholders like `[ACCOUNT_NUMBER_1]`.
- Hooks the `message_end` event to swap any placeholders back to their original values in the assistant's finalized message before pi displays / persists it.
- Identical values reuse the same placeholder for the whole session.

## Install

```bash
cd pi-privacy-filter
npm install   # or: bun install
```

Then wire it into pi using any one of:

### Quick test
```bash
pi -e ./index.ts
```

### Project-local
```bash
mkdir -p .pi/extensions
ln -s "$PWD" .pi/extensions/pi-privacy-filter
```

### Global
```bash
mkdir -p ~/.pi/agent/extensions
ln -s "$PWD" ~/.pi/agent/extensions/pi-privacy-filter
```

### Or via pi settings (`~/.pi/settings.json`)
```json
{
  "extensions": ["/absolute/path/to/pi-privacy-filter"]
}
```

## Commands

- `/privacy-mapping` — dump the current placeholder→value mapping (handy for debugging).

## Files

- `index.ts` — the extension
- `sample.ts` — original standalone POC (`bun run sample.ts`)