Claude Code on Real Codebases: WordPress, PHP & Legacy Code

This course contains the use of artificial intelligence.

Almost every Claude Code tutorial starts with an empty folder. Most developers do not get to work that way. You inherit a codebase somebody else wrote years ago, with conventions nobody wrote down and a test suite you would rather not break, and that is where the agent has to earn its keep.

This course spends all four hours inside one of those. The codebase is Easy Digital Downloads, a WordPress ecommerce plugin of roughly 240,000 lines of PHP, GPL-2.0, with a full PHPUnit suite and a live issue tracker. You clone a pinned fork, so your checkout matches the videos line for line. After that, everything is real: real open issues, real diffs, real test runs, and the failures an agent produces when it meets a codebase this size and gets it wrong.

The course assumes about two years of professional development experience. You should be comfortable in a terminal and in git, able to read PHP, and able to look at a diff and say whether it is correct. If you want a site built or fixed without writing code, this is the wrong course, and it is better to find that out now than after you buy.

What you work through

• Setup and the honest gate. What Claude Code costs in practice, installing it on macOS, Windows or Linux, and one command that takes the course test suite to a known baseline.

• Onboarding a codebase you did not write. Why a naive first prompt falls apart on a large repo, how to map an unfamiliar architecture, what to tell the agent to ignore, and how to write project instructions that measurably change its behaviour. The module ends on a genuine open issue, closed and reviewed.

• The working loop. Plan mode used properly, turning a vague ask into a spec, sessions and compaction, checkpoints and rewind, git as the layer you recover from, and watching token cost on a big repo.

• When it goes wrong. Five failure modes, each triggered on purpose and shown in full: the plausible-but-wrong fix, the silently dropped requirement, the refactor that keeps the suite green while breaking behaviour, the over-engineered five-liner, and the runaway loop. Then a five-minute review pass that catches all five, and the rules each failure earns in your project instructions.

• Verification and trust. Tests as the agent's feedback loop. The changes you never merge unreviewed. A review checklist packaged as a reusable skill, permissions and sandboxing set up as real controls, and a security pass over a finished diff.

• Extending Claude Code for one codebase. Skill, MCP server, hook or plugin: when each is the right answer, then building all four against real conventions in this repo.

• Capstone. One real open issue from spec to pull request, including the part where it goes wrong and gets recovered.

Easy Digital Downloads is the worked example rather than the subject. It earned the slot by being large, ordinary in its mess, and reachable in one command. The same patterns apply to WooCommerce and other ecommerce plugins, and to any hook-heavy PHP codebase. What you are learning is what to tell the agent, what to check, and what to refuse. That travels to any language.

What is included

• 44 lectures, about four hours of video

• Downloadable notes for every lecture, with each command and prompt written out

• A commands cheat-sheet and a 69-term glossary

• A companion kit of 81 files: project instruction files and their full evolution, prompts, the failure scenarios, the review checklist, the skill, the hook, the MCP configuration and the diffs

• A "Before you start" text lecture covering tool versions, substitutes and the whole setup

Who this is not for

Beginners and non-programmers. Anyone shopping for a feature tour. If you have never had to work in code you did not write, the course will not land, because that problem is its entire subject.

How this course was made. The narration is a synthetic voice, generated from scripts written by the instructor. Every screen recording, prompt, diff and test run is real and was captured as it happened; nothing on screen is staged or generated.

This course is an independent educational project. It is not affiliated with, endorsed by, or sponsored by the maintainers of Easy Digital Downloads, the codebase used as its worked example, or by the makers of Claude Code.