session-agent-builder

session-agent-builder is an agent for Claude Code from agentlas-ai/Agentlas-OS. It costs 32 tokens per session (1,303 once invoked), scanned A, original, Apache-2.0.

A builder that turns an interactive work session into a reusable Agentlas agent. It extracts the useful method and removes private conversation details and project-specific information.

In plain words
What is it for?
Creating a reusable agent from a conversation, including its procedure, decisions, checks, failure handling, and success criteria.
Why use it?
It preserves a successful way of working without carrying confidential or one-off session data into the new agent.

Agent for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: mentions Claude Code; mentions Codex.

Part of the hephaestus plugin — 4 agents, 6 hooks shipped together

Good fit Creating a reusable agent from a conversation, including its procedure, decisions, checks, failure handling, and success criteria.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/agentlas-ai/agentlas-os/session-agent-builder
About the project

Agentlas OS is a local-first system for creating, storing, borrowing, and running specialist AI agents and temporary agent teams through supported hosts and models. It serves people who want reusable agents that remain available across computers and model workspaces, and the catalogue contains its skills, commands, hooks, agents, instructions, plugin, and rule.

agentlas-ai/Agentlas-OS · 1,588 stars · on GitHub · agentlas.cloud

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.

Clone the repo
git clone --depth 1 https://github.com/agentlas-ai/Agentlas-OS

Made for: Claude Code.

Or install hephaestus, the plugin that ships this one along with the rest of its 4 agents, 6 hooks.

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 session-agent-builder

README.md
[![agentmods](https://agentmods.dev/badge/agents/agentlas-ai/agentlas-os/session-agent-builder/github.svg)](https://agentmods.dev/agents/agentlas-ai/agentlas-os/session-agent-builder)
Your own site
<a href="https://agentmods.dev/agents/agentlas-ai/agentlas-os/session-agent-builder"><img src="https://agentmods.dev/badge/agents/agentlas-ai/agentlas-os/session-agent-builder/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.

agentmods 80×15 button for session-agent-builder

Your own site · 80×15
<a href="https://agentmods.dev/agents/agentlas-ai/agentlas-os/session-agent-builder"><img src="https://agentmods.dev/badge/agents/agentlas-ai/agentlas-os/session-agent-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 32 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,303 The whole file, excluding the scripts and references it only reads on demand.
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 $0.00032 $0.01303
Opus 5.5 $0.00013 $0.00521
Sonnet 5.5 $0.00006 $0.00261
Haiku 4.5 $0.00003 $0.00130

Measured 8d ago against content hash 82a3e046c5b3, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

session-agent-builder 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.

claude/plugins/agentlas-core-engine-meta-agent/agents/session-agent-builder.md · 134 lines

How it starts

The opening of the file, as written. The whole thing — 134 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Session Agent Builder

Mission

Turn the current host conversation into a reusable Agentlas agent. Extract the goal, useful reasoning, working procedure, decisions, corrections, failures, success criteria, and validation habits. Generalize them into a standalone agent prompt and package while removing session-specific identity, project details, private data, and hidden instructions.

This is the fourth canonical Hephaestus builder. It owns the interactive /hep-build session route and reuses the existing single-agent builder by default. An explicit owner choice is required before producing a team shape.

Input rule

For an interactive host, the current conversation is the source. It includes the visible user and assistant turns and relevant visible outcomes from this same thread. The owner does not need to create, export, attach, or paste a JSON file. Do not search recent sessions, host databases, or another conversation to reconstruct the source.

The deterministic runner's JSON/JSONL source route remains available for terminal, replay, and headless use when the owner explicitly supplies a file. That is an implementation boundary, not the interactive /hep-build session UX. Do not infer a recent session, host database, or another conversation when the current interactive context is unavailable.

Interactive procedure

  1. Ask the destination question first:

    이 세션에서 만든 에이전트를 기본 전역 Agentlas 에이전트 폴더에 만들까요? 다른 위치를 원하면 경로를 알려주세요. 별도 위치를 지정하지 않으면 전역 폴더에 만듭니다.

    Use AGENTLAS_AGENT_HOME when configured, otherwise ~/.agentlas/agentlas-agent. Create a new child package under that home, using a safe slug derived from the approved capability. If the child already exists, ask for another name or an explicit destination; never overwrite it. Do not ask for a generic PACKAGE_TARGET or a JSON export in this route.

  2. Analyze the current conversation in two passes. The first pass produces a Generalized Session Report with these sections:

    • Capability and goal
    • When to use
    • Core principles
    • Operating procedure
    • Decision rules in IF / THEN / BECAUSE / AVOID / INSTEAD form
    • Tool usage by purpose, not literal command
    • Validation and completion criteria
    • Failure modes and rejected approaches
    • Lessons from owner corrections
    • Output expectations
    • Privacy and generalization constraints

Read the full file on GitHub · 134 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 Changed 82a3e046c5b3
  2. 1mo ago First seen · 134 lines · 32 tokens per session scan A 76619398b46f

Subscribe to this mod's changes

session-agent-builder is an agent published in the GitHub repository agentlas-ai/Agentlas-OS (1,588 stars, last pushed 4d ago), licensed Apache-2.0. It adds 32 tokens to every session and 1,303 once invoked, about $0.0001 per session on Opus 5.5. 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.