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/v0.22.0/abcop-0.22.0-aarch64-apple-darwin.tar.gz
tar -xzf abcop-0.22.0-aarch64-apple-darwin.tar.gz
sudo cp abcop-0.22.0-aarch64-apple-darwin/abcop /usr/local/bin/
sudo mkdir -p /usr/local/share/man/man1
sudo cp abcop-0.22.0-aarch64-apple-darwin/abcop.1 /usr/local/share/man/man1/

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

# example for v0.22.0 — use the asset name from the release page
curl -LO https://github.com/adrianov/abcop/releases/download/v0.22.0/abcop_0.22.0-1_amd64.deb
sudo dpkg -i abcop_0.22.0-1_amd64.deb
man abcop

Related MCP server: genpark-cyclomatic-complexity-refactoring-scout-skill

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 new unit inside a human head and an LLM context window. An existing unit may stay over that ceiling when the edit does not raise its score. 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. Knobs: --max-abc and --max-module-abc. --full and --everything report every hit, not only the current edit.

• 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 method counting matches RuboCop 1.89 byte-for-byte (scripts/compare_parity.py). A block outside a method (match do, before do, a class-level each) is its own unit; each / map / select still roll into the block that contains them.

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; rises and edited functions only
abcop --format jsonl lib > abcop.jsonl # streaming CI / agent input
abcop --only used-once src             # inline candidates in edited functions
abcop --max-abc 12 --only abc lib      # stricter function budget
abcop --full lib                       # every function over the ceiling, every local
abcop --everything lib                 # same report, with no default pruning
abcop --max-module-abc 80 lib          # stricter module budget
abcop --sort-by-score --only abc lib   # worst first
abcop --uncommitted                    # pre-commit; rises and edited functions only
abcop --mr --only abc                  # branch files; still only ABC rises vs HEAD
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. Findings still follow the edit filter below.

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 the 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.

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.

What a normal scan reports

Every scan except --full and --everything compares the working tree to HEAD:

• AbcSize reports a method over --max-abc only when its score is strictly higher than the same method in HEAD (same name, source order). A score that stayed the same or fell stays quiet, including a legacy method that was already over the ceiling. A method that exists only in the working tree counts as an increase. The message asks to return to the previous score when that score was already over the ceiling (rose from 20 to 21 -- back to 20 or below). When HEAD was under the ceiling, the target is the ceiling (rose from 16.28 to 21.28 -- back to 17 or below).

• UsedOnce / NeverUsed report only inside a function whose text changed against HEAD. A local in a function the edit did not touch stays quiet. Locals outside any function still report.

• ModuleAbcSize reports a module over --max-module-abc only when its whole-file score is strictly higher than that file in HEAD. A score that stayed the same or fell stays quiet, including a legacy module already over the ceiling. A file that does not exist in HEAD is held to the ceiling. The message asks to return to the previous score when that score was already over the ceiling (rose from 200 to 210 -- back to 200 or below). When HEAD was under the ceiling, the target is the ceiling.

• No HEAD blob (not a git checkout, or an untracked file) reports every method over the ceiling, every local, and every module over the ceiling.

--uncommitted and --mr also drop function and local findings on lines the diff did not touch.

Whole-tree report

--full and --everything report every method over --max-abc, every local, and every production module over --max-module-abc. ModuleAbcSize still exempts test trees on those runs. --full keeps the default skips. --everything lifts gitignore, hidden directories, and vendored/generated/test pruning. ignore in the user config still applies to both.

User config

One file holds user options. It is $XDG_CONFIG_HOME/abcop when that variable is set, otherwise ~/.config/abcop. $ABCOP_CONFIG replaces the path. Nothing is written into the project.

ignore is a gitignore pattern, one option per line, applied in every project relative to that project's root. A directory pattern covers everything inside it. Naming the path, --full, and --everything do not bring a match back. An MCP inspection of a matched path is empty.

ignore = app/services/legacy/
ignore = lib/old.rb

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.

Caching

Content-addressed cache under $XDG_CACHE_HOME/abcop (or ~/.cache/abcop; override with ABCOP_CACHE_DIR). Warm reruns ~5× faster. Keys cover contents, version, rule revision, threshold, checks and path — no cross-project collisions. Auto-pruned to 20 000 entries; --no-cache disables. Nothing is written inside the project.

Supported languages

Seventeen languages plus embedded JS in HTML/templates, four rules each, one CI gate.

Named declarations are measured units; anonymous function-likes roll into the enclosing unit; nested units never double-count. C-family: file-scope globals are out of single-file reach; loop-head locals are protocol; field writes also read the object; export-macro class forms (class UTIL_EXPORT Foo) are skipped for variable rules.

Benchmarks

Apple M1 Pro, warm cache:

¹ --cache false — rubocop's own cache otherwise makes repeats look free.

Development

cargo test
cargo build --all-targets   # zero warnings
abcop src                   # dogfood

Shared engine: src/scope_model/ (backend, walk, eval); language collectors sit beside each backend (clike/, sollang/, …). Probe grammar nodes with abcop --dump-tree FILE. Parity: scripts/compare_parity.py.

License

GNU GPL v3 or later (SPDX: GPL-3.0-or-later). See LICENSE.

Copyright © 2026 Peter Adrianov. All rights reserved.