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joern-mcp: Instructions file for Claude Code

CLAUDE.md

joern-mcp CLAUDE.md is an instructions file for Claude Code from BlockSecCA/joern-mcp. It costs 347 tokens per session, scanned A, original, MIT.

Project instructions for Joern MCP, a local server that connects an AI assistant to Joern, a code-analysis tool used for security reviews.

In plain words
What is it for?
Use them when developing or reviewing the Joern connection, MCP tools, query handling, or project configuration.
Why use it?
They explain the server’s architecture, required design document, commands, and behavior when Joern is unavailable.

Instructions file for Claude Code

Written for Claude Code: the file is CLAUDE.md. Also seen: mentions Claude Code.

This is BlockSecCA/joern-mcp's own configuration. It tells Claude Code how to work on joern-mcp itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything joern-mcp configures →

not rated 5repo 1mo ago A scan 347 tokens original MIT
View source ↗ BlockSecCA/joern-mcp
Reuse

Borrowing it

Nothing to install: this file belongs to BlockSecCA/joern-mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/BlockSecCA/joern-mcp/main/CLAUDE.md
Clone the repo
git clone --depth 1 https://github.com/BlockSecCA/joern-mcp

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for joern-mcp CLAUDE.md

README.md
[![agentmods](https://agentmods.dev/badge/instructions/blocksecca/joern-mcp/claude-md.svg)](https://agentmods.dev/instructions/blocksecca/joern-mcp/claude-md)
Your own site
<a href="https://agentmods.dev/instructions/blocksecca/joern-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/blocksecca/joern-mcp/claude-md.svg" alt="Measured on agentmods" height="20"></a>
Per session 347 This file is loaded in full into every session.
When invoked 347 The same file — it is already loaded in full.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00347 $0.00347
Opus 5 $0.00173 $0.00173
Sonnet 5 $0.00069 $0.00069
Haiku 4.5 $0.00035 $0.00035

Measured 7d ago against content hash 180222e60b24, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

joern-mcp CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 52 lines

What it actually says

joern-mcp

What This Is

STDIO MCP server that wraps a local Joern instance for AI-driven code security analysis. Claude Code talks to this server, this server talks to Joern's HTTP API.

Architecture

Claude Code <--stdio--> joern-mcp (TypeScript) <--HTTP--> Joern server (JVM, port 8080)

Joern is installed at ~/.local/share/joern/joern-cli/ and available as joern on PATH.

Stack

  • TypeScript, ES modules
  • @modelcontextprotocol/sdk for MCP
  • Node built-in fetch for HTTP to Joern (no external HTTP lib needed)

Commands

npm run build    # tsc
npm run dev      # tsc --watch
npm start        # node dist/index.js

Project Structure

src/
  index.ts          # MCP server entry point (stdio transport)
  joern-client.ts   # HTTP client for Joern server API
  tools/            # MCP tool handlers (one file per tool group)
docs/
  mcp-spec.md       # Full design spec with tool definitions

Design Spec

Read docs/mcp-spec.md before writing any code. It defines all tools, the query execution pattern, and configuration.

Conventions

  • Fail loudly if Joern server is not reachable
  • All queries go through the synchronous POST /query-sync endpoint
  • Environment variables for config (JOERN_HOST, JOERN_PORT, timeouts)
  • No process management — joern-mcp does NOT start/stop Joern
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 7d ago First seen · 52 lines · 347 tokens per session scan A 180222e60b24

Subscribe to this mod's changes

joern-mcp CLAUDE.md is an instructions file published in the GitHub repository BlockSecCA/joern-mcp (5 stars, last pushed 1mo ago), licensed MIT. It adds 347 tokens to every session, about $0.0017 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

code-securitycpgjoernmcpstatic-analysis
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