---
name: read-before-edit-guard
title: Read-before-edit — gate before file modification
description: "Skill enforcing Read before every Edit/Write in the same session. Eliminates \"blind edits\" based on memory — every file the agent modifies must have been read in the current session. Protects against overwriting others' work."
category: review
tags:
  - read-first
  - harness
  - safety
  - edycja
  - dyscyplina
requires:
  - Claude Code
  - Read tool
source: https://madejski.ai/skilloteka/read-before-edit-guard
locale: en
license: MIT
---

# Read-before-edit — gate before file modification

## Rule

**Every file you modify must have been read in the same session.**

Not in the previous session. Not "sometime". **In this session.**

## Why

- Files change between sessions (you or another agent commit changes)
- Agent memory is unreliable
- Overwriting without reading = losing someone else's work
- Edit tools require exact match — without reading the latest version, Edit fails

## Flow

```
About to modify file X?
  └── Did you read X in this session?
        ├── YES → Edit / Write
        └── NO  → Read X first, then Edit / Write
```

## Practical rules

### 1. Read before the first Edit in a session

### 2. Re-read after long operations (build, subagent, branch switch, lots of time)

### 3. Write-new-file doesn't require Read — but Glob first to make sure the file doesn't exist

### 4. Bulk edit via sed/awk — forbidden

Without reading the diff is unknown. Regex on production code = risk. Edit tool has exact match, safer.

## Red flags

- "From memory I know this file has function X" → re-read
- "I'm editing a file I haven't opened but I know what it does" → STOP, Read
- "I'll skip Read, I know the structure" → memory is lying to you, Read
- "File hasn't changed since my last Read 30 min ago" → maybe it did, Read

## What to do when Edit fails on "string not found"

You have a stale snapshot in memory:

1. **Re-read** the file fresh
2. Find the current fragment
3. Update `old_string` to current content
4. Edit again

**DO NOT** try different regex, `replace_all: true` "to make it work", or sed/awk fallback.

## Integration with other harness skills

- **Plan-before-code**: plan lists files to edit — each must be Read first
- **Phase continuity brief**: brief shows commits since last session → files requiring Read before touching
- **Tool failed → STOP**: Edit fail = tool failed = STOP and diagnose (re-read)

## Effect

- Zero overwritten work
- Zero "magical" merge conflicts
- Edit always works on first try
- Session audit trail shows Read → Edit pair per file