Borrowing it
Nothing to install: this file belongs to eclipse-rdf4j/rdf4j. 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/eclipse-rdf4j/rdf4j/main/.agent/skills/hotspot-jit-forensics/SKILL.mdgit clone --depth 1 https://github.com/eclipse-rdf4j/rdf4jWrote 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/eclipse-rdf4j/rdf4j/hotspot-jit-forensics)<a href="https://agentmods.dev/skills/eclipse-rdf4j/rdf4j/hotspot-jit-forensics"><img src="https://agentmods.dev/badge/skills/eclipse-rdf4j/rdf4j/hotspot-jit-forensics/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/eclipse-rdf4j/rdf4j/hotspot-jit-forensics"><img src="https://agentmods.dev/badge/skills/eclipse-rdf4j/rdf4j/hotspot-jit-forensics.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00064 | $0.01164 |
| Opus 5 | $0.00032 | $0.00582 |
| Sonnet 5 | $0.00013 | $0.00233 |
| Haiku 4.5 | $0.00006 | $0.00116 |
Grade A, and why
hotspot-jit-forensics 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 8d 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.
How it starts
The opening of the file, as written. The whole thing — 147 lines — stays where its author put it; the contents beside it link to each section on GitHub.
HotSpot C2 / JIT Forensics & Optimization
A practical playbook for diagnosing Java performance issues by looking at what HotSpot actually does.
Use this skill when you suspect:
- Lost inlining, megamorphic dispatch, or deoptimization.
- A hot method is slow because it never reaches C2.
- High CPU in tiny methods (often a no-inline or missed intrinsic).
- High allocation rate or cache-unfriendly object layout.
- Compilation failures/bailouts (node limits, method too big, deep inlining).
- Code cache pressure, safepoint stalls, or lock contention.
Quick start (repeatable artifacts)
- Collect JVM facts
.codex/skills/hotspot-jit-forensics/scripts/jit-facts.sh --out jit-facts.txt
For a running process:
.codex/skills/hotspot-jit-forensics/scripts/jit-facts.sh --pid <pid> --out jit-facts.txt
- Generate a C2 directives file
.codex/skills/hotspot-jit-forensics/scripts/jit-directives.sh \
--method "com/foo/MyClass.myMethod()" \
--out c2-directives.json5
- Run the target command with compiler logging
.codex/skills/hotspot-jit-forensics/scripts/jit-run-log.sh \
--directives c2-directives.json5 \
--logfile jit.xml \
-- java -XX:+UnlockDiagnosticVMOptions -jar app.jar
Artifacts produced:
jit-facts.txt(version, flags, OS/arch, optional jcmd output)c2-directives.json5(method-scoped compiler diagnostics)jit.xml(HotSpot compilation log)- Console output with inlining and assembly (if
hsdisis available)
Core workflow
1) Profile first (do not guess)
Use JFR or async-profiler to identify the actual hot method(s).
2) Confirm compilation tier
Determine if the method is interpreted, C1, or C2.
Runtime:
jcmd <pid> Compiler.codelist | head
jcmd <pid> Compiler.queue
jcmd <pid> Compiler.codecache
Start-up (noisy):
java -XX:+PrintCompilation -jar app.jar
3) Capture inlining + compilation decisions for ONE method
Prefer Compiler Directives with a focused match.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 8d ago First seen · 147 lines · 64 tokens per session scan A c690582d6fea
hotspot-jit-forensics is a skill published in the GitHub repository eclipse-rdf4j/rdf4j (412 stars, last pushed yesterday), licensed BSD-3-Clause. It adds 64 tokens to every session and 1,164 once invoked, about $0.0003 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 2026-09-03.
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