AI-assisted PCB design for KiCad 10

TL;DR Highlight

Konnect exposes KiCad to Claude via MCP tools in one Rust binary, cutting listing context from 23K to 2K tokens

Who Should Read

A developer whose MCP server has so many tools that context tokens are a burden, and who wants to automate hardware design with LLM agents

Core Mechanics

Listing all tools costs 23K tokens
- The README says exposing all 228 tools costs about 23K tokens of context on every listing.
- Konnect's router loads only a starter kit of about 2K tokens first.
- The model pulls in toolsets on demand.
Call path shrank to one function call
- The original KiCAD-MCP-Server went through TypeScript, a Python subprocess, JSON over stdin/stdout, and SWIG C++ proxies.
- In Konnect a tool call is a function call inside one process and one language.
- It ships as a single static binary of 20-25 MB, about 9 MB to download.
IPC API for PCB, direct file editing for schematics
- PCB edits use KiCad 10's IPC API (protobuf over NNG) and integrate with KiCad's undo/redo.
- Schematic .kicad_sch files are edited by its own S-expression engine.
- Writes are atomic (write, fsync, rename) to avoid corrupting files.
The model can diagnose its own tool failures
- Built-in observability includes get_recent_calls, server_stats, and JSONL call logs.

Community Reactions

Many reported routing is the weak spot
- One user tried computer-use, then mixed it with this repo and found stackup and part config great but routes terrible.
- It snakes traces through SMD pins and makes 10-30 tiny bends instead of two 45-degree turns.
- They said KiCadRoutingTools produces more sensible routes.
Works if you hand-route and hand back
- One user said Fable 5.1 pins a few key traces and lets freerouting do the rest.
- Pushing hard for carefully designed routes makes it write code and get better results.
- They still need to review it and route a few traces by hand.
A high-altitude balloon tracker came out well
- One user had Fable design a 4-layer board and used a tournament-style routing system to lock in good routes.
- It handled JLCPCB part search, spec checks, and manufacturing output, while Opus did not quite reach a good board.
- They stressed domain knowledge helps.
Unusual parts cause big mistakes

How to Apply

Split your MCP tools into toolsets
- Today, measure your MCP server's tool listing in tokens.
- Group the heavy tools by purpose and expose only a few core ones at startup.
- Add a load_toolset-style tool to fetch the rest on demand.
Log tool calls as JSONL
- Record each tool call's name, arguments, and error as one JSONL line.
- Expose a get_recent_calls-style tool to the model.
- Let it check the cause itself when a call fails.
Switch file-editing tools to atomic writes
If an LLM tool edits files, write to a temp file, fsync, then rename.
- Add round-trip tests before and after edits to catch corruption.
- Keep a human review step for weak stages such as routing.

Try It

copy & run

# Paste into Claude Code or Claude Desktop: simplified version of Konnect's toolset split

I'm building an MCP server. The tool list below is fully exposed now and uses a lot of context.

{{tool names and descriptions}}

Redesign it as follows.
1. Group the tools into 5-8 toolsets by purpose and name them.
2. Pick a minimal starter kit (10 tools or fewer) to expose at startup.
3. Write JSON-schema specs for load_toolset(name) and list_toolsets().
4. Also write the input/output schema for a get_recent_calls tool for failure diagnosis.

Next to try: compare the token count of the tool list before and after the redesign.

Terminology

MCPModel Context Protocol, a standard for LLMs to call external tools. Think of it as a USB port for LLMs.

KiCad IPC APIThe official channel for external programs to remote-control a running KiCad editor. Edits show up as if made by hand and support undo.

S-expressionA text format of nested parenthesized lists. KiCad schematic files use it.

Freerouting / Specctra DSN·SESFreerouting is an automatic PCB router. DSN is the input file describing the routing problem and SES is the result file.

atomic writeA way of writing files so an interruption never leaves a half-written file. Write to a temp file, then rename it into place.