A coding agent, except the codebase is a circuit board

What it does

Copperhead is a CLI agent that treats hardware design like software: it reads and edits real .kicad_sch and .kicad_pcb files (plain s-expression text), keeps markdown design docs as its memory, and runs kicad-cli ERC/DRC checks after every edit until they pass. copperhead do "<change>" works on an existing KiCad repo the way Cursor works on a codebase; copperhead create goes from a natural-language brief all the way to gerbers, a firmware scaffold, and a dev plan.

The interesting bit

The discipline is the product. Two hard gates: the agent literally cannot touch a KiCad file until a validated change proposal exists, and nothing counts as done until the ERC/DRC tools agree. Propagation — the boring step where you change one value and it must ripple through every doc and schematic that references it — is exactly what they’ve automated.

Key highlights

• Spec-gated in, verification-gated out: every edit traces to a documented intent, and drift becomes a build failure
• copperhead check runs ERC, DRC, doc-drift, and spec validation with no LLM calls — CI-safe
• export bom produces supplier-ready CSVs for JLCPCB, DigiKey, and Mouser, deterministically and offline, and refuses to export if BOM.md disagrees with the schematic
• Model-agnostic: works with Claude Code, Cursor Agent, or Codex saved logins, or plain OpenAI/Anthropic API keys, plus any OpenAI-compatible endpoint
• Every real decision gets a one-line rationale written next to it, so future changes don’t quietly undo past reasoning

Caveats

• Self-described as early: Phase 1 is implemented, and the spec is the source of truth — expect the surface to move before 1.0
• copperhead create still uses hardcoded stages rather than the skill system
• The Codex sandbox can technically read files like .env, and Codex session logs live outside copperhead’s redaction boundary — worth knowing for sensitive repos

Verdict

If you maintain a KiCad project and already live in an AI coding agent, this is a genuinely fresh application of the pattern. If you don’t know what ERC stands for, move along.