
CLAUDE.md and AGENTS.md: What Coding Agents Read
How Claude Code and Codex load project instruction files, what belongs in them, and a worked AGENTS.md for a small Next.js repo.
How to build an AI agent, test it, and keep it running: frameworks, development environments, memory, tools and MCP, and Codex and Claude Code in practice.

People use “agent development environment” to mean three different things: a coding product, a practice world where an agent gets scored as it learns (an RL environment), or the place an agent's code actually runs. Start with the guide to all three. Then look at the RL environment projects, or keep the short definition handy.
New to this? Read these in order.
Build a small ticket-label agent in stages: define its boundaries, add retrieval and state, then test failure and recovery. Each lesson has an exercise and a concrete deliverable.
Download the local lab. The downloadable Python 3.10+ lab uses only the standard library and synthetic data. Run python3 agent_lab.py for eight boundary tests. It makes no network or model calls and does not establish production readiness.
All labs on GitHub. Every lesson's lab, with a script that runs them all and checks each result against the recorded one.

How Claude Code and Codex load project instruction files, what belongs in them, and a worked AGENTS.md for a small Next.js repo.

Install Marker, convert a PDF, read the output, then do the same through the Datalab API. Every command comes from the official READMEs and docs.

Which documents a person should check, how many to spot-check, how many reviewer hours you need, and how corrections make the system better.

Per-page prices for Datalab, Extend, Azure, Google and LLM APIs as of September 2026, and a worked example showing why human review is most of the bill.

What changed when document parsing moved from OCR to AI models that read the whole page, with dated examples from Datalab, Extend, Azure and Google.

Thirty document AI terms, from OCR and parsing to precision, review thresholds and per-page pricing, each linked to the post where it matters.

How Extend's extraction schemas, test sets and workflows fit together, from its docs, with a worked schema for one made-up invoice.

Extend, Datalab, Google, Azure and Mistral compared on one disclosed invoice task, using only documented features and published prices.

Branches, commits, worktrees and pull requests with a coding agent, plus the git actions an agent should never take without you.

Run Claude Code and Codex non-interactively and in GitHub Actions: flags, the GitHub app, Codex cloud, secrets, and a worked workflow.

How Claude Code and Codex hooks work, the settings.json shape, and a worked hook that runs your checks before the agent commits.

Install Claude Code and Codex, sign in, give each the same broken test to fix in a practice project, and check what it changed before you keep it.

Add an MCP server to Claude Code and Codex, using GitHub's official server in read-only mode as the example, and decide what the agent may do.

Check how accurate your invoice extraction really is, field by field, with a small answer key and a tested Python script that scores every field.

The four document AI operations, what each returns, and when each is the right tool, walked through one synthetic two-page invoice.

When to make a coding agent plan before it edits, how plan mode works in Claude Code and Codex, and how to cut a feature into small checkable tasks.

Read an agent's change in the right order: tests, deletions, dependencies and config first. A review checklist for Claude Code and Codex.

Write one SKILL.md that works in Claude Code, Codex and Cursor, and learn when a skill beats another line in CLAUDE.md or AGENTS.md.

Subagents, worktrees, and parallel lanes in Claude Code and Codex: how to split work so files don't collide, and what to review.

Run four small agent shapes on fake support tickets and watch what each one does when a step fails, stalls or gets an unclear request.

Compare a Python agent backend, a LangGraph chat UI and a full-stack chatbot, then check one starter at a fixed version without paying for model calls.

Run a local Pydantic Evals test, then see how Promptfoo, LangSmith, Braintrust and plain Python handle the same ten tickets and the same scoring rules.

Make a Claude Messages API request in Python, validate its JSON response, and test authentication, rate limits and bad output with local fixtures.

Run ten support-ticket cases through two simple classifiers, score what they got wrong, and keep every failure in the report.

Build an approval step in SQLite that refuses changed, outdated, expired or revoked requests, and never repeats finished work on retry.

Run a four-step ticket workflow that checks its plan first, caps how much work it does, can be canceled, and shows what a failed step blocks.

Build a SQLite memory store that keeps users apart, catches outdated updates, records where each value came from, and handles expiry and deletion.

Build a six-document RAG pipeline, check its citations, filter out private and outdated documents, and measure the synonym question it misses.

Build a small Python MCP server and client, find a ticket-label tool, and test good calls, rejected inputs and protocol errors.

Build a Python loop where a model asks for tools and your code decides what runs, with argument checks, hard limits and ten repeatable test cases.

Use Cursor to build a small ticket-review screen, then check that approving, refusing an outdated change and retrying all work in the browser and over HTTP.

Use Copilot in VS Code to fix a small SQLite delete bug. Start from two failing tests, then check the one line of SQL that matters in the patch.

Run a small Python webhook receiver on your own machine, check each request's signature, store it safely, and test what happens with duplicates and crashes.

Write three prompts with a fixed output shape, then check twelve good and bad example answers against them with a small Python script.

Five open projects for building practice tasks and scoring for coding agents, what each one covers, and what to check before you trust a score.

Wire a real HTTP receiver to document lookup and a stored approval, then run twelve local tests of what happens when steps fail or repeat.

Reactive agents wait to be asked. Proactive agents notice things on their own. How each is built, where each breaks, and which one to start with.

Set up a research agent so every claim keeps its source, guesses are labeled as guesses, and the brief ends in a decision someone can check.

People mean three things by agent development environment: a coding agent, a place to train one, or a sandbox to run its code. Here's how to tell them apart.

Five enterprise agent platforms compared on who acts, what's saved, how they connect and who runs them, plus one pilot test to give every finalist.

Datalab, ABBYY, Rossum, Google and Azure for pulling data out of documents, and the questions that decide which one fits your team.

Compare Glean, Guru, Notion and Microsoft knowledge search on who can see what, how fast changes show up, and whether answers hold up in a pilot.

Seven steps to take an AI agent from your laptop to real users: hosting, storage, tests, spending limits, and how to find out when it goes wrong.

What Model Context Protocol is, how AI apps use it to reach tools and data under the 2026-07-28 spec, who runs it, and how to start using or building a server.

Build a multi-agent AI system: give each agent one job, pick a pattern and a framework, check every handoff, and test before you launch.