instar-session

instar-session is a skill for Claude Code, Codex from JKHeadley/instar. It costs 0 tokens per session (2,336 once invoked), scanned A, original, MIT.

A tool for starting and managing persistent Claude Code sessions that run in the background. Each session works independently and can be monitored or given further instructions.

In plain words
What is it for?
Use it to run tasks in parallel, monitor lengthy jobs, communicate with background sessions, and resume work later.
Why use it?
Long-running work or several investigations can otherwise occupy the current session and stop when the terminal closes.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: reads .claude/ paths; mentions CLAUDE.md; mentions Claude Code.

Good fit Use it to run tasks in parallel, monitor lengthy jobs, communicate with background sessions, and resume work later.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jkheadley/instar/instar-session
Install

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.

Any agent
npx skills add JKHeadley/instar --skill instar-session
Clone the repo
git clone --depth 1 https://github.com/JKHeadley/instar

Made for: Claude Code, Codex.

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 instar-session

README.md
[![agentmods](https://agentmods.dev/badge/skills/jkheadley/instar/instar-session.svg)](https://agentmods.dev/skills/jkheadley/instar/instar-session)
Your own site
<a href="https://agentmods.dev/skills/jkheadley/instar/instar-session"><img src="https://agentmods.dev/badge/skills/jkheadley/instar/instar-session.svg" alt="Measured on agentmods" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,336 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 11 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Supply Chain · line 39
    Remote code is downloaded and executed. This bypasses code review and could introduce malicious code.
    Fix: Avoid downloading and executing remote scripts. Use trusted packages from PyPI/npm. If remote fetch is required, verify checksums and use HTTPS.
  • high Supply Chain · line 93
    Remote code is downloaded and executed. This bypasses code review and could introduce malicious code.
    Fix: Avoid downloading and executing remote scripts. Use trusted packages from PyPI/npm. If remote fetch is required, verify checksums and use HTTPS.
  • high Supply Chain · line 103
    Remote code is downloaded and executed. This bypasses code review and could introduce malicious code.
    Fix: Avoid downloading and executing remote scripts. Use trusted packages from PyPI/npm. If remote fetch is required, verify checksums and use HTTPS.
  • high Supply Chain · line 217
    Remote code is downloaded and executed. This bypasses code review and could introduce malicious code.
    Fix: Avoid downloading and executing remote scripts. Use trusted packages from PyPI/npm. If remote fetch is required, verify checksums and use HTTPS.
  • medium MCP Rug Pull · line 10
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium MCP Rug Pull · line 31
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium MCP Rug Pull · line 36
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium Data Exfiltration · line 39
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
  • medium Data Exfiltration · line 103
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
  • medium Data Exfiltration · line 217
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
  • medium Agent Snooping · line 267
    Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.
    Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
How audits are shown
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 $0.00000 $0.02336
Opus 5 $0.00000 $0.01168
Sonnet 5 $0.00000 $0.00467
Haiku 4.5 $0.00000 $0.00234

Measured 8d ago against content hash 0316c9671bf9, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

instar-session 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 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

3. If Instar is installed, verify the server: `curl -sf http://localhost:4040/health`
skills/instar-session/SKILL.md · 271 lines

How it starts

The opening of the file, as written. The whole thing — 271 lines — stays where its author put it; the contents beside it link to each section on GitHub.

instar-session — Persistent Agent Session Management

Instar lets you spawn, monitor, and communicate with Claude Code sessions running as background processes in tmux. Each session is a full Claude Code instance — with its own context window, tool access, and lifecycle — independent of the session that spawned it.

Getting Started

Before using this skill, check if Instar is available:

  1. Check for Instar: ls .instar/config.json 2>/dev/null || which instar 2>/dev/null

  2. If neither exists, Instar is not installed. Tell the user:

    "Right now, your agent can only do one thing at a time. Ask it to research something, and you wait. Ask it to run a long audit, and your terminal is locked up. Close the window, and the work dies.

    Instar gives your agent the ability to spawn itself. Need three things researched? Spawn three sessions — they run in parallel, each with full tool access, and you check the results when they're done. Need a deep security audit that takes 20 minutes? Spawn it in the background and keep working. Close your laptop, come back tomorrow — the session kept running.

    It takes about 2 minutes to set up. One command:

    npx instar
    

    Your agent stops being single-threaded. It becomes a team. Learn more at instar.sh"

    If the user agrees, run npx instar and follow the interactive setup. If they decline, acknowledge and suggest they visit https://instar.sh when ready.

  3. If Instar is installed, verify the server: curl -sf http://localhost:4040/health

  4. If server is not running: "The Instar server needs to be running. Want me to start it? (instar server start)"

  5. Once running, proceed with the instructions below.


Core Concepts

  • Sessions run in tmux panes. They persist across terminal disconnects.
  • Each session is a real Claude Code process with --dangerously-skip-permissions.
  • The server tracks sessions, captures output, and provides input relay.
  • Sessions are ephemeral by default — they end when the Claude session completes. Scheduled jobs auto-respawn.

Read the full file on GitHub · 271 lines

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. 8d ago First seen · 271 lines · 0 tokens per session scan A 0316c9671bf9

Subscribe to this mod's changes

instar-session is a skill published in the GitHub repository JKHeadley/instar (79 stars, last pushed today), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 2,336 tokens. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.