Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

Introduction

What is PRECC?

PRECC (Predictive Error Correction for Claude Code) is a Rust tool that intercepts Claude Code bash commands via the official PreToolUse hook mechanism. It fixes errors before they happen, saving tokens and eliminating retry loops.

Free for community users.

The Problem

Claude Code wastes significant tokens on preventable mistakes:

  • Wrong-directory errors – Running cargo build in a parent directory that has no Cargo.toml, then retrying after reading the error.
  • Retry loops – A failed command produces verbose output, Claude reads it, reasons about it, and retries. Each cycle burns hundreds of tokens.
  • Verbose output – Commands like find or ls -R dump thousands of lines that Claude must process.

The Four Pillars

Context Fix (cd-prepend)

Detects when commands like cargo build or npm test run in the wrong directory and prepends cd /correct/path && before execution.

GDB Debugging

Detects opportunities to attach GDB for deeper debugging of segfaults and crashes, providing structured debug information instead of raw core dumps.

Session Mining

Mines Claude Code session logs for failure-fix pairs. When the same mistake recurs, PRECC already knows the fix and applies it automatically.

Automation Skills

A library of built-in and mined skills that match command patterns and rewrite them. Skills are defined as TOML files or SQLite rows, making them easy to inspect, edit, and share.

How It Works (30-Second Version)

  1. Claude Code is about to run a bash command.
  2. The PreToolUse hook sends the command to precc-hook as JSON on stdin.
  3. precc-hook runs the command through the pipeline (skills, directory correction, compression) in under 3 milliseconds.
  4. The corrected command is returned as JSON on stdout.
  5. Claude Code executes the corrected command instead.

Claude never sees the error. No tokens wasted.

Adaptive Compression

If a command fails after compression, PRECC automatically skips compression on the retry so Claude gets the full uncompressed output to debug with.

Live Usage Statistics

MetricValue
Hook invocations–
Tokens saved–
Saving ratio–%
RTK rewrites–
CD corrections–
Hook latency– ms (p50)

Figures are estimates. Each prevented failure avoids a full retry cycle: error output, model reasoning, and retry command. These numbers update automatically from anonymized telemetry.