CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

Nuclei is a modern, high-performance vulnerability scanner built in Go that leverages YAML-based templates for customizable vulnerability detection. It supports multiple protocols (HTTP, DNS, TCP, SSL, WebSocket, WHOIS, JavaScript, Code) and is designed for zero false positives through real-world condition simulation.

Development Commands

Building and Testing

• make build - Build the main nuclei binary to ./bin/nuclei

• make test - Run unit tests with race detection

• make integration - Run integration tests (builds and runs test suite)

• make functional - Run functional tests

• make vet - Run go vet for code analysis

• make tidy - Clean up go modules

Validation and Linting

• make template-validate - Validate nuclei templates using the built binary

• go fmt ./... - Format Go code

• go vet ./... - Static analysis

Development Tools

• make devtools-all - Build all development tools (bindgen, tsgen, scrapefuncs)

• make jsupdate-all - Update JavaScript bindings and TypeScript definitions

• make docs - Generate documentation

• make memogen - Generate memoization code for JavaScript libraries

Testing Specific Components

• Run single test: go test -v ./pkg/path/to/package -run TestName

• Integration tests are in integration_tests/ and can be run via make integration

Architecture Overview

Core Components

• cmd/nuclei - Main CLI entry point with flag parsing and configuration

• internal/runner - Core runner that orchestrates the entire scanning process

• pkg/core - Execution engine with work pools and template clustering

• pkg/templates - Template parsing, compilation, and management

• pkg/protocols - Protocol implementations (HTTP, DNS, Network, etc.)

• pkg/operators - Matching and extraction logic (matchers/extractors)

• pkg/catalog - Template discovery and loading from disk/remote sources

Protocol Architecture

Each protocol (HTTP, DNS, Network, etc.) implements:

• Request interface with Compile(), ExecuteWithResults(), Match(), Extract() methods

• Operators embedding for matching/extraction functionality

• Protocol-specific request building and execution logic

Template System

• Templates are YAML files defining vulnerability detection logic

• Compiled into executable requests with operators (matchers/extractors)

• Support for workflows (multi-step template execution)

• Template clustering optimizes identical requests across multiple templates

Key Execution Flow

1. Template loading and compilation via pkg/catalog/loader

2. Input provider setup for targets

3. Engine creation with work pools for concurrency

4. Template execution with result collection via operators

5. Output writing and reporting integration

JavaScript Integration

• Custom JavaScript runtime for code protocol templates

• Auto-generated bindings in pkg/js/generated/

• Library implementations in pkg/js/libs/

• Development tools for binding generation in pkg/js/devtools/

Template Development

• Templates located in separate nuclei-templates repository

• YAML format with info, requests, and operators sections

• Support for multiple protocol types in single template

• Built-in DSL functions for dynamic content generation

• Template validation available via make template-validate

Key Directories

• lib/ - SDK for embedding nuclei as a library

• examples/ - Usage examples for different scenarios

• integration_tests/ - Integration test suite with protocol-specific tests

• pkg/fuzz/ - Fuzzing engine and DAST capabilities

• pkg/input/ - Input processing for various formats (Burp, OpenAPI, etc.)

• pkg/reporting/ - Result export and issue tracking integrations