Building a Regex Engine with a team of parallel Claudes

February 10, 2026

Inspired by Nicholas Carlini’s C compiler agent team experiment.

TL;DR

I tasked two Opus 4.6 agents to build a regex engine, then walked away. Here is the repo.

Over 14 Claude Code sessions, the agent team wrote ~1700 lines of code, and now I have a working Rust regex engine:

kian@Kian regex %   cargo run -- "a+b*" "xxaaabbbzz"
   Compiling regex-engine v0.1.0 (/Users/kian/Developer/regex)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.06s
     Running `target/debug/regex-engine 'a+b*' xxaaabbbzz`
MATCH:aaabbb

Setup

This experiment required three separate pieces:

A remote which the agents could push to and build their work
A server for running the agents on the cloned remote (the original experiment uses Docker containers; I do not)
A third directory (which is my main contribution) called regex that with the harnessing not provided by the original post, namely:

AGENT_PROMPT.md
launch_agents.sh
agent_loop.sh

Workflow

I ran two agents in parallel with a loop script.

Each agent loop does:

Clone the repo into workspace-<agent_id> if not already.
git pull --rebase origin main.
Run Claude on yolo mode with the shared prompt.
Append session output to per-agent log files.
Sleep briefly and repeat.

Coordination primitives in the repo:

current_tasks/ for lock files (task claiming)
notes/ for handoffs and caveats
PROGRESS.md for shared status updates

Analysis

Where the real work happened

The implementation progress came from a small number of successful sessions:

bootstrap to 37/38 tests
harness fix and edge tests to 54/54
optimization and robustness to 69/69
hardening and expanded coverage to 159/159

Coordination

The lock-file mechanism using current_tasks/ was generally effective, but there were a few cases where stale locks required cleanup.

Two things that helped

using oracle-based testing against the Python re library
preserving modular boundaries (parser → abstract syntax tree → compiler → virtual machine)

Replication

If you would like to replicate these results, it suffices to:

git clone git@github.com:kiankyars/parallel-ralph.git
mv parallel-ralph/regex .
# rm -rf parallel-ralph
chmod 700 regex/*.sh
./regex/launch_agents.sh 2

The above assumes you have the Claude Code CLI installed on your machine, along with screen and a few other standard Linux packages.

Future Work

Today I am building SQLite from scratch, but this time I’m going to use both Codex and Claude on the same project to see how heterogeneous agents interact with each other. I considered using a lock TTL (time to live) and automatic stale-lock cleanup to prevent agents from being blocked by abandoned lock files.

Multi-agent

I’m thinking of having specialized agent roles as well. Here is what Carlini did:

I tasked one agent with coalescing any duplicate code it found. I put another in charge of improving the performance of the compiler itself, and a third I made responsible for outputting efficient compiled code. I asked another agent to critique the design of the project from the perspective of a Rust developer, and make structural changes to the project to improve the overall code quality, and another to work on documentation.

Appendix

Code size

Counted files: 6 (.rs + .sh)
Total lines: 1,680
Approx. code lines (non-blank, non-comment): 1,331
Rust: 1,328 total / 1,091 code lines
Shell: 352 total / 240 code lines

Agent sessions

Total logged sessions: 1,273
Agent 1 sessions: 519
Agent 2 sessions: 754
Rate-limit-only sessions: 1,259
Non-rate-limited sessions: 14

Usage

Tokens: In 9.4k / Out 6.5k (I realize now that this is completely erroneous, but this is what Claude Code said the token usage was. Their token tracker is not working.)
Used ~30% of my Claude Pro weekly limit

Notes on the Anthropic approach

For context, this is the initial commit on the Anthropic repo, and this is the first page of commits.

Citation

@misc{kyars2026regex,
  author = {Kian Kyars},
  title = {Building a Regex Engine with a team of parallel Claudes},
  year = {2026},
  month = feb,
  day = {10},
  howpublished = {\url{https://kiankyars.github.io/machine_learning/2026/02/10/regex.html}},
  note = {Blog post}
}