cpg-analysis

Overview of cpg-analysis skill

cpg-analysis is a deep code analysis skill for situations where a normal repository skim is not enough. It helps you reason about control flow, data flow, program dependencies, taint paths, and security findings using Joern CPG and CodeQL. If you are doing a security review, tracing a bug across functions, or proving how input reaches a sink, this is the cpg-analysis skill to use.

Best fit: security audits and flow tracing

Use cpg-analysis for Security Audit work, especially when you need to answer questions like “Can this input reach a dangerous sink?” or “What paths exist from source to sink across multiple files?” It is most useful when the job is evidence-backed analysis, not surface-level code explanation.

What makes it different

Unlike a generic prompt, cpg-analysis is designed around graph-based reasoning: AST for structure, CFG for execution order, and data-flow graphs for propagation. The practical difference is better traceability for security and correctness questions, especially in larger codebases where a simple grep or summary misses the real path.

When it is worth installing

Install cpg-analysis when you expect to work repeatedly with deep static analysis, taint tracking, or vulnerability hunting. If you only need quick code navigation, tier-1 memory tools are usually enough and lighter to run.

How to Use cpg-analysis skill

Install cpg-analysis and confirm the runtime

Install the cpg-analysis skill with the repo’s skill manager, then verify you have the required runtime for the path you plan to use. Joern-based workflows typically need Docker and a JVM; CodeQL-based workflows need the CodeQL CLI. If you cannot run those tools locally or in your environment, the skill will be limited regardless of prompt quality.

Start from the right files

Begin with SKILL.md, then read the sections that describe tier selection, when to use Joern, and the key MCP tools. Those parts tell you which analysis path to choose before you spend time generating queries. If the skill references a specific repository tree, follow that map first instead of guessing from memory.

Turn a vague request into a usable prompt

The best cpg-analysis usage starts with a concrete analysis target, not just “analyze this repo.” Include:

• the repository or subdirectory
• the language or framework if known
• the security question or bug hypothesis
• the source, sink, or feature you care about
• any constraints, such as “no runtime execution” or “focus on auth flow”

Example prompt shape:
Use cpg-analysis to trace whether user-controlled input from the API reaches command execution in src/ without sanitization. Focus on interprocedural paths and show the key nodes and files.

Use a staged workflow

A strong cpg-analysis guide usually works best in two passes: first map the relevant surfaces, then drill into paths. Start broad enough to locate entry points and candidate sinks, then narrow to the exact functions or files involved. That approach reduces false confidence and keeps the output tied to the actual data flow.

cpg-analysis skill FAQ

Is cpg-analysis only for security work?

No. Security is the clearest fit, but the skill also helps with bug hunts, execution-path reasoning, and understanding how values move through a complex codebase. It is most valuable when the question depends on control flow or data flow rather than simple text matching.

Do I need Joern and CodeQL for every use?

Not always. Joern is typically the better first choice for CPG-based exploration, while CodeQL is stronger when you want interprocedural security queries or vulnerability patterns. Pick the tool that matches the question instead of running both by default.

Is cpg-analysis beginner-friendly?

It is usable by beginners, but only if the task is specific. A vague request will produce vague analysis. If you can name the file, the input source, and the risky sink, the cpg-analysis skill becomes much easier to use well.

When should I not use cpg-analysis?

Do not reach for cpg-analysis when you only need documentation lookup, basic refactoring advice, or a quick summary of one file. It is an install-costly skill, so it pays off when the analysis is deep enough to justify graph-based tooling.

How to Improve cpg-analysis skill

Give the analysis a narrower target

The most important improvement is to narrow scope. “Find security issues” is too broad; “trace whether request params in routes/ can reach exec or SQL query construction” is far better. Clear source and sink definitions make cpg-analysis output more actionable and reduce wasted traversal.

Share the constraints that matter

If your environment blocks Docker, if the codebase is polyglot, or if you only want static analysis, say so up front. Constraints change the feasible workflow and prevent the skill from suggesting paths you cannot run. For cpg-analysis install decisions, this is often the difference between useful and unusable.

Ask for evidence, not conclusions

When iterating, ask for the chain: entry point, intermediate functions, graph nodes, and final sink. That forces the response to show the reasoning that matters in a cpg-analysis for Security Audit review. If the first pass is too broad, refine by naming the file set or the specific query type you want next.

Re-run with a better hypothesis

If the first result is noisy, improve the hypothesis instead of asking for a generic second pass. For example, replace “find auth issues” with “trace unauthenticated access from the router to the sensitive handler, excluding test code and mocks.” Strong hypotheses are the fastest way to get higher-signal cpg-analysis usage.