What is elm327_obd_for_mac CLAUDE.md?

A set of development rules for a native macOS Ford diagnostic tool written in Rust. The tool communicates with ELM327 USB adapters to read vehicle data and perform Ford-specific diagnostics.

It guides work on serial communication, ELM327, OBD-II vehicle diagnostics, and Ford diagnostic features, using a tests-first development cycle.

It gives contributors a consistent way to build the project while keeping it tested, compilable, and focused on tracked GitHub issues.

How TheTom/elm327_obd_for_mac configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to TheTom/elm327_obd_for_mac. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/TheTom/elm327_obd_for_mac/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/TheTom/elm327_obd_for_mac

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

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Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

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Per session 4,418 This file is loaded in full into every session.

When invoked 4,418 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.04418	$0.04418
Opus 5.5	$0.01767	$0.01767
Sonnet 5.5	$0.00884	$0.00884
Haiku 4.5	$0.00442	$0.00442

Measured 2mo ago against content hash 8c60997992bd, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

elm327_obd_for_mac CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 653 lines

How it starts

The opening of the file, as written. The whole thing — 653 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

Ford Diagnostic Tool — Autonomous Development Rules

Native macOS Ford Diagnostic Tool — a Rust CLI that communicates directly with ELM327 USB adapters for Ford-specific OBD-II and UDS diagnostics on Apple Silicon. No Wine, no Windows. See PRD.md for full product spec.

Core thesis:

Most Ford owners can't run FORScan on macOS without painful Wine hacks. Build a native Rust tool that talks directly to ELM327 adapters and the truck's CAN bus.

This repository is developed using test-driven, autonomous execution with strict guardrails.

Core Operating Principles

Tests before implementation — mandatory.
Every piece of work must correspond to a GitHub Issue.
Implement the smallest working solution.
No unsafe unless justified — if you write unsafe, comment why.
Keep architecture simple and extensible.
Keep the repository compilable at all times.
Maintain organized documentation, repository maps, and test maps.
Follow the issue → failing tests → implementation → review → commit → close issue loop.
Focus on serial communication, ELM327 protocol, OBD-II, and Ford-specific diagnostics.
If uncertain about a requirement, create a GitHub Issue and continue with other unblocked work.

GitHub Issue-Driven Development (MANDATORY)

This project uses GitHub Issues as the bug/task system, modeled after Google Buganizer.

Every unit of work is treated as an issue.

This includes:

features
bugs
implementation tasks
investigations
product questions
refactors
architectural decisions
hardware compatibility findings

Issue Requirement (MANDATORY)

Before starting any work:

Ensure a GitHub Issue exists
Assign the correct priority label
Assign the correct type label
Assign the correct area label(s)
Write failing tests
Only then may implementation begin

No task may be worked on without a corresponding issue.

Priority Labels (Buganizer Style)

Read the full file on GitHub · 653 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 653 lines · 4,418 tokens per session scan A 8c60997992bd

Subscribe to this mod's changes

elm327_obd_for_mac CLAUDE.md is an instructions file published in the GitHub repository TheTom/elm327_obd_for_mac (16 stars, last pushed 7mo ago), licensed Apache-2.0. It adds 4,418 tokens to every session, about $0.0177 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Hardware and IoT

elm327_obd_for_mac CLAUDE.md next to 6 instructions from other repositories
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elm327_obd_for_mac: Instructions file for Claude Code