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.
curl -O https://raw.githubusercontent.com/BlockSecCA/joern-mcp/main/.claude/skills/joern-analysis/SKILL.mdgit clone --depth 1 https://github.com/BlockSecCA/joern-mcpWrote 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.
[](https://agentmods.dev/skills/blocksecca/joern-mcp/joern-analysis)<a href="https://agentmods.dev/skills/blocksecca/joern-mcp/joern-analysis"><img src="https://agentmods.dev/badge/skills/blocksecca/joern-mcp/joern-analysis/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/blocksecca/joern-mcp/joern-analysis"><img src="https://agentmods.dev/badge/skills/blocksecca/joern-mcp/joern-analysis.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00036 | $0.02125 |
| Opus 5 | $0.00018 | $0.01063 |
| Sonnet 5 | $0.00007 | $0.00425 |
| Haiku 4.5 | $0.00004 | $0.00213 |
Grade A, and why
joern-analysis scanned grade A with 1 finding 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 9d 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.
Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
call.name("eval|exec|system|popen|spawn|passthru|shell_exec|child_process") How it starts
The opening of the file, as written. The whole thing — 244 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Joern Security Analysis
Guide for using the joern-mcp tools to analyze code for security issues.
Prerequisites
Joern must be running as a server before using any tools:
joern --server
Always start with check_connection to verify Joern is reachable.
Workflow
1. Connect and import
check_connection → verify Joern is up
import_code(path, name) → build the CPG (slow, minutes for large projects)
list_projects → see what's loaded
switch_project(name) → activate a previously imported project
2. Explore the codebase
get_methods(filter?) → list methods, optionally filtered by name
get_types(filter?) → list classes/types
get_calls(methodName?) → find call sites
get_source(methodName) → read a method's source code
get_parameters(methodName)→ see parameter types and names
3. Navigate relationships
get_callers(methodName) → who calls this method?
get_callees(methodName) → what does this method call?
get_base_classes(className) → parent/base classes (inheritance chain)
get_derived_classes(className) → child classes (all implementations)
4. Security analysis
find_vulnerabilities(categories?) → structural pattern scan (reconnaissance)
taint_analysis(source, sink) → trace data flow from source to sink
reachable_by(source, sink) → check if sink is reachable from source
get_data_flows(source, sink) → get all flow paths between two points
Recommended flow: find_vulnerabilities first to identify interesting patterns, then taint_analysis to confirm exploitability with full data flow paths.
5. Raw queries
query(cpgql) → run arbitrary CPGQL for anything not covered above
CPGQL Expression Reference
For taint_analysis, reachable_by, and get_data_flows, source and sink are CPGQL expressions relative to cpg.. They get wrapped as:
val source = cpg.<your_expression>; val sink = cpg.<your_expression>; sink.reachableByFlows(source).p
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.
- 9d ago First seen · 244 lines · 36 tokens per session scan A ea556c0ff320
joern-analysis is a skill published in the GitHub repository BlockSecCA/joern-mcp (5 stars, last pushed 2mo ago), licensed MIT. It adds 36 tokens to every session and 2,125 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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