abcop

A must-have gate for AI-written code. Agents ship faster than humans can re-read; abcop keeps that code understandable by gating function and module ABC complexity so every unit fits a human head and an LLM context window. Diagnostics are also a hook for automated refactoring — extract a method, split a module — so CI rejects bad growth and points agents at concrete maintainability fixes.

One self-contained binary across Ruby, Rust, Python, Go, PHP, Java, C#, Dart, JavaScript, TypeScript, C, C++, Objective-C, Swift, Solidity, Zig and Haskell — no runtimes, no plugins, no per-language installs. Written in Rust for speed: one parse per file, one walk per metric, grammars compiled in; whole trees in milliseconds.

Install

brew install adrianov/abcop/abcop

cargo install abcop

macOS (.tar.gz from GitHub Releases; binary + man):

# Apple Silicon — use the *-x86_64-apple-darwin.tar.gz asset on Intel Macs
curl -LO https://github.com/adrianov/abcop/releases/download/v0.18.5/abcop-0.18.5-aarch64-apple-darwin.tar.gz
tar -xzf abcop-0.18.5-aarch64-apple-darwin.tar.gz
sudo cp abcop-0.18.5-aarch64-apple-darwin/abcop /usr/local/bin/
sudo mkdir -p /usr/local/share/man/man1
sudo cp abcop-0.18.5-aarch64-apple-darwin/abcop.1 /usr/local/share/man/man1/

Ubuntu / Debian (.deb from GitHub Releases; amd64, Ubuntu 22.04+ / Debian bookworm+):

# example for v0.18.5 — use the asset name from the release page
curl -LO https://github.com/adrianov/abcop/releases/download/v0.18.5/abcop_0.18.5-1_amd64.deb
sudo dpkg -i abcop_0.18.5-1_amd64.deb
man abcop

Example run

lib/sinatra/base.rb:1254:0: C: Metrics/AbcSize: Assignment Branch Condition size for `error_block!` is too high. [<7, 14, 9> 18.06/17]
src/main.rs: W: Metrics/ModuleAbcSize: Assignment Branch Condition size for module is too high. [<80, 200, 60> 228.04/120] -- extract a coherent subunit
132 files analysed in 0.09s, 7 abc offenses, 0 used-once offenses, 0 never-used warnings, 14 module-abc warnings

Why ABC, not line counts

Line counts lie. The ABC metric (Jerry Fitzpatrick, C++ Report, June 1997) counts what does work — assignments (A), branches (B), conditions (C) — as sqrt(A² + B² + C²). Fitzpatrick defined both method and module scope; abcop gates both:

A sparse wrapper and a dense god-object can share a line count; ABC separates them. Complexity is the gate — never a line budget. UsedOnce / NeverUsed are secondary.

Built for AI workflows

• Understandable by construction. AbcSize 17 and ModuleAbcSize 120 keep every unit inside a human head and an LLM context window. Models edit small units reliably; when something breaks, the blast radius is tiny.
• Refactoring hook. Exit code 1 plus stable JSON/JSONL diagnostics (rule, score, vector, message) feed agents and scripts: split oversized modules, extract hot methods. Each finding is an actionable maintainability step, not a style nit.
• Fast enough for every push. Sub-second whole-tree scans — including code an agent will never re-read tomorrow.
• Signal only. No formatting or style cops. Vendored, generated and test trees are skipped by default. Two knobs: --max-abc and --max-module-abc.
• Prefer MCP with LLMs. abcop --mcp is the best way to use abcop from an agent: the model gets offenses as soon as it writes, so it can fix complexity and dead locals in the same turn and ship effective code right away — not after a later CLI/CI pass. Official Rust rmcp SDK; tool abcop_inspection. Listed on the MCP Registry as io.github.adrianov/abcop (crates.io package + each GitHub v* tag).

Inspired by RuboCop (Ruby AbcSize parity and # rubocop:disable directives) and lizard (one tool, many languages). Ruby's counting matches RuboCop 1.89 byte-for-byte (scripts/compare_parity.py).

Advantages

• ~850k–940k LOC/s per core (Apple M1 Pro). RuboCop's lib tree (943 files, 110k LOC): 0.13 s — ~39× faster than rubocop --only Metrics/AbcSize (cache off), ~140× a full rubocop run.
• One binary, zero deps — grammars and an embedded result cache (cache.redb) compiled in; works on clean CI images with no language toolchains.
• Deterministic — same findings every run; text / JSON / JSONL stream as files finish; --sort-by-score buffers for worst-first emit.

Usage

abcop [OPTIONS] PATH...

Exit codes: 0 clean, 1 findings, 2 usage error.

abcop app lib                          # two trees
abcop --format jsonl lib > abcop.jsonl # streaming CI / agent input
abcop --only used-once src             # inline candidates
abcop --max-abc 12 --only abc lib      # stricter function budget
abcop --max-module-abc 80 lib           # stricter module budget
abcop --sort-by-score --only abc lib   # worst first
abcop --uncommitted                    # pre-commit / agent loop
abcop --mr --only abc                  # this branch's touched units
abcop --mcp                            # MCP server on stdio (for AI clients)

JSON diagnostics include file, line, column, severity, rule, message, plus score / vector for ABC rules:

{"rule":"Metrics/AbcSize","score":10.0,"vector":"<6, 8, 0>"}
{"rule":"Metrics/ModuleAbcSize","score":120.5,"vector":"<40, 100, 40>"}

Scope selection

Named paths — those targets only.

Omitted — narrowest useful scope, announced on stderr:

1. uncommitted work vs HEAD if the tree is dirty
2. else current MR (--mr forces this)
3. else full tree (outside a repo)

Default walks prune test/fixture trees, vendored/build output (vendor/, node_modules/, target/, …), db/migrate/, route tables (config/routes.rb, config/routes/*.rb), and generated names (*.min.js, *_pb.go, …). Name a path explicitly to scan it anyway. Third-party, route-table, and fixture paths are never scoped review surface — a diff through vendor/ or tests/fixtures/ does not make that material owned code.

Scoped ModuleAbcSize re-sums only methods that intersect the diff and compares that total to --max-module-abc (default 120; untracked = every method). A small patch into an oversized legacy file stays quiet unless the touched methods themselves exceed the ceiling; AbcSize still reports any changed method over --max-abc. Full scans (--full, --everything) report every production module over the ceiling; ModuleAbcSize still exempts test trees on full scans (scoped runs can flag them when changed methods sum over the limit). UsedOnce / NeverUsed always follow the changed lines.

On a dirty tree the bare default is uncommitted-only; --mr takes the full branch union. Commits straight to main use a 36-hour window when no branch base applies. --uncommitted fails outside a repository instead of silently widening.

Directives

Everywhere except Rust, RuboCop-style # / // suppressions work (trailing and block; bare Metrics allowed). rubocop:disable-next is ignored, matching rubocop.

def legacy_path # rubocop:disable Metrics/AbcSize
  ...
end

MCP (Model Context Protocol)

Preferred for LLM / agent workflows. Wire abcop as an MCP server so the model can call abcop_inspection while it edits: feedback arrives in the same turn, the agent corrects soon, and it writes maintainable code on the first pass instead of discovering ABC / UsedOnce / NeverUsed only in CI.

abcop --mcp runs a long-lived MCP server on stdio — same idea as RuboCop’s MCP and rrubocop, with no Ruby mcp gem. Tool:

• MCP Registry name: mcp-name: io.github.adrianov/abcop

Metadata lives in server.json, which is part of the Cargo package on crates.io. Each GitHub v* release tag publishes that listing to the MCP Registry (after the crates.io upload).

Example client config (Cursor / VS Code / Windsurf):

{
  "mcpServers": {
    "abcop": {
      "type": "stdio",
      "command": "abcop",
      "args": ["--mcp"],
      "cwd": "/path/to/your/project"
    }
  }
}

Claude Code:

claude mcp add abcop -- abcop --mcp

Intended for MCP clients, not interactive use.