Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/heapy/kortex/jshellnpx skills add Heapy/kortex --skill jshellgit clone --depth 1 https://github.com/Heapy/kortexWhat 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 | $0.00024 | $0.00491 |
| Opus 5 | $0.00012 | $0.00246 |
| Sonnet 5 | $0.00005 | $0.00098 |
| Haiku 4.5 | $0.00002 | $0.00049 |
Grade A, and why
jshell 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 yesterday.
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.
What it actually says
JShell
Run JShell in an agent-controlled terminal and own its lifecycle. Record its pid when it starts, keep the terminal session, and do not finish the task until that session has exited.
Resolve the executable
Run jshell --version before the first evaluation. On macOS, /usr/bin/jshell can be a launcher
that reports no Java runtime even when an SDK-managed JDK is installed. In that case, resolve an
installed JDK and use its absolute bin/jshell path for the rest of the task.
If a requested JShell option is uncertain, inspect that executable's --help or --help-extra.
Start and use JShell
Start this command in a terminal with TTY enabled, replacing the final argument with the resolved absolute path:
/bin/sh -c 'printf "JSHELL_PID=%s\n" "$$" >&2; exec "$1" --execution local --feedback concise' sh /absolute/path/to/jshell
Save both the returned terminal-session id and the printed JSHELL_PID. exec replaces the shell
with JShell without changing the pid, while --execution local keeps evaluation in that tracked
process.
Send Java snippets to the terminal session with a trailing newline. Poll a running session with an empty write. A returned live-session id only means the command is still running; it does not prove that JShell is waiting at a prompt.
Finish the session
Never send /exit. When no more evaluation is needed:
- From a separate terminal command, send
TERMto the recorded numeric pid. For example, if JShell printedJSHELL_PID=16438, runkill -TERM 16438. - Poll the original terminal session with empty writes for at most five seconds.
- If it has not exited after those five seconds, confirm that the same pid is still the tracked
JShell process, send
KILLto that pid, and poll the original session again until it exits.
Never abandon a live JShell terminal session. Do not use pkill jshell or killall; terminate only
the pid recorded for the current task.
What ships with it
1 file 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.
- yesterday First seen · 48 lines · 24 tokens per session scan A bbd745316aa5
jshell is a skill published in the GitHub repository Heapy/kortex (5 stars, last pushed 4d ago), licensed Apache-2.0. It adds 24 tokens to every session and 491 once invoked, about $0.0001 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.
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