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chestertons-fence SKILL.md skillA

chestertons-fence from rjmurillo/ai-agents is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.

Install it, pinned

mdr add rjmurillo/ai-agents/chestertons-fence@v1.1.0

Pins v1.1.0 in mdr.lock. Pin the fingerprint instead.

Audit grade: A, 17 of 17 checks passed
Kind: SKILL.md skill
Repository: rjmurillo/ai-agents
Path: .claude/skills/chestertons-fence/SKILL.md
Versions recorded: 5
Latest version: v1.1.0, committed Sep 25, 2026
First version recorded: Jul 22, 2026
Size: 8,200 bytes
Repository stars: 48
License: MIT

Investigate historical context of existing code, patterns, or constraints before proposing changes. Automates git archaeology, PR/ADR search, and dependency analysis to prevent removing structures without understanding their purpose. Use when you ask "why does this code/constraint exist", "is it safe to remove this". Do NOT use for forward-risk analysis (use pre-mortem).

Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.

What the file says

# Chesterton's Fence Investigation

Enforce epistemic humility before changing existing systems. Understand original purpose before proposing changes.

## Quick Start

```text
# Investigate why code exists before changing it
/chestertons-fence "path/to/file.py" "remove unused validation"

# Investigate an ADR before deprecating it
/chestertons-fence "docs/architecture/ADR-005.md" "allow bash scripts"
```

## Triggers

| Phrase | Context |
|--------|---------|
| `why does this exist` | Investigating existing code or patterns |
| `chestertons fence` | Explicit investigation request |
| `before removing` | Planning deletion or replacement |
| `investigate history` | Researching original rationale |
| `prior art investigation` | ADR-required investigation |

## Quick Reference

| Input | Output | Destination |
|-------|--------|-------------|
| File path or ADR number | Investigation report | `.project-toolkit/analysis/NNN-chestertons-fence-TOPIC.md` |
| Component description | Historical context summary | stdout (JSON) |

## When to Use

Use this skill BEFORE proposing changes to existing:

- Code patterns or architectural decisions
- ADRs, constraints, or protocol rules
…

Read the whole file at its exact version.

How to install

The exact contents, by fingerprint

mdr add rjmurillo/ai-agents/chestertons-fence@sha256:6801ea292f90226e

The line at the top of this page pins the label v1.1.0, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.

Badge

[![mdr](https://markdownregistry.com/badge/art_wnkv4jfynzx5ding.svg)](https://markdownregistry.com/a/art_wnkv4jfynzx5ding)

3 badge image fetches in 30 days. What the badge shows.

Versions

The registry has recorded 5 versions of this file, between Jul 22, 2026 and Sep 25, 2026, about one every 16 days.

version	committed	commit	size	audit
v1.1.0 latest	2026-09-25	3fda96c	8,200 B	A	view · diff
v1.1.0	2026-09-23	0eb2c32	8,027 B	A	view · diff
v1.1.0	2026-09-23	efd148e	6,635 B	A	view · diff
v1.1.0	2026-09-15	696280a	6,590 B	A	view · diff
v1.1.0	2026-07-22	e7a63be	6,526 B	A	view

Audit of the latest version

A 17 of 17 checks passed. Fixed automatic checks with no AI involved, so the same checks give the same answer every run.

pass: Frontmatter block present
pass: Frontmatter declares a name
pass: Frontmatter declares a description
pass: Size between 200 bytes and 200 KB (8200 bytes)
pass: No zero-width or bidi control characters
pass: No instruction hidden inside an HTML comment
pass: No link to an exfiltration or paste host
pass: No credential-shaped string
pass: No instruction to send local credentials anywhere
pass: No text hidden with inline styles
pass: No prompt-injection phrasing
pass: No curl or wget piped into a shell
pass: No recursive delete of root, home or parent
pass: No instruction to read or print local credentials
pass: No base64 blob over 200 characters
pass: No link to a raw IP address
pass: No script tag

Source

GitHub

rjmurillo/ai-agents · 48 stars · license MIT · pushed 2026-10-20 · branch main

API

GET https://markdownregistry.com/api/v1/artifacts/art_wnkv4jfynzx5ding
GET https://markdownregistry.com/api/v1/resolve?ref=rjmurillo/ai-agents/chestertons-fence
GET https://markdownregistry.com/api/v1/blob/6801ea292f90226ec34eb52d6c3e76c6d51d52ff28b889976136cfb2c1b4e6fe

Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.

Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.