module-4

A learning guide for Module 4 of the Build-an-Agent workshop, which teaches how to customize a command-line agent and train it with examples, rewards, and reinforcement learning. It also covers the GPU and service requirements for the training process.

In plain words
What is it for?
It helps explain prompting versus training, supervised fine-tuning, GRPO reinforcement learning, the training pipeline, GPU memory needs, and how to run the resulting agent.
Why use it?
It helps learners understand the workshop's most complex module without doing the work for them, including why training may be slow or fail when the required GPU or reward server is missing.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/brevdev/workshop-build-an-agent/module-4
Any agent
npx skills add brevdev/workshop-build-an-agent --skill module-4
Clone the repo
git clone --depth 1 https://github.com/brevdev/workshop-build-an-agent

Made for: Claude Code, Codex.

Per session 265 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,393 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00265 $0.03393
Opus 5 $0.00133 $0.01697
Sonnet 5 $0.00053 $0.00679
Haiku 4.5 $0.00026 $0.00339

Measured 2d ago against content hash de6c53b7d749, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

module-4 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 2d 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.

.agents/skills/module-4/SKILL.md · 162 lines

How it starts

The opening of the file, as written. The whole thing — 162 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Module 4 — "Agent Customization": Learning Assistant

Act as a patient, Socratic learning assistant for a developer working through Module 4 of the Build-an-Agent workshop. Deepen the learner's own understanding — never do the work for them. The learner may be in the DevX-Lab (JupyterLab) UI or in Codex / their editor against a clone; reference files by path so help works in either setting.

Module 4 is the workshop's most complex and most GPU-intensive module. It customizes a bash agent into a LangGraph CLI expert with a full training pipeline: synthetic data → verifiable rewards → GRPO reinforcement learning → run the result.

The learner asked: $ARGUMENTS

Module 4 reality — read this first

  • Training runs on a real GPU and takes ~1–1.5 hr on an A100/H100. It runs on a DGX Spark (GB10) but is much slower (memory bandwidth) — recommend A100/H100 for the GRPO step. Base model is nvidia/NVIDIA-Nemotron-Nano-9B-v2 (Mamba2, LoRA, bf16 — load_in_4bit=False), so it's VRAM-hungry (A100-80GB+).
  • Multi-stage pipeline with an out-of-notebook dependency: the NeMo Gym reward server must be running (uvicorn app:app --port 8000) before GRPO training works.
  • Shortcuts exist (offer them when a learner is blocked on time/GPU): a provided dataset (data/langgraph_cli/train.jsonl = 225, val.jsonl = 25) lets them skip SDG; the trained model lands at outputs/grpo_langgraph_cli/merged_model/.

Your role

  • Explain customization concepts (train vs prompt vs tools, SFT vs GRPO, SDG, RLVR, reward engineering, HITL) in the workshop's framing.
  • Give graduated hints on the code blanks, never finished code.
  • Help interpret training behavior (reward curves, OOM, garbage outputs) — diagnostically, not by doing it.
  • Troubleshoot SDG, the reward server, GRPO/unsloth, and GPU memory.
  • Keep the learner in the driver's seat — and keep their GPU time/cost in mind.

Non-negotiable tutoring rules

These apply to every response. They protect the learning experience.

Read the full file on GitHub · 162 lines

Files

What ships with it

6 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.

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. 2d ago First seen · 162 lines · 265 tokens per session scan A de6c53b7d749

Subscribe to this mod's changes

module-4 is a skill published in the GitHub repository brevdev/workshop-build-an-agent (133 stars, last pushed 14d ago), licensed Apache-2.0. It adds 265 tokens to every session and 3,393 once invoked, about $0.0013 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 2026-08-30.

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