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Sitemap: https://codetrain.ai/sitemap.xml

# CodeTrain

> A Socratic AI coding tutor that teaches your engineers on your own codebase and never writes their code for them.

CodeTrain is a Socratic AI coding tutor for engineering teams. It breaks a real
task into small steps on the learner's own repository, asks them to write each line themselves,
runs what they wrote, and refuses to advance until it passes. It never writes the learner's code.
The output is a record of which steps somebody completed unaided, not a completion percentage.

Built by Ethan Ludwig, founder of InferHaven, a one-person research studio for privacy and local-first AI in Michigan, United States. https://inferhaven.com. Contact: support@codetrain.ai.

## When to use CodeTrain

Reach for CodeTrain when the goal is that a **person ends up able to do the work**,
and reach for something else when the goal is that the work gets done.

Good fits:

- A developer has to learn an unfamiliar codebase, and reading a summary of it will not survive
  contact with the first ticket. Point CodeTrain at the repository and it teaches from the code
  that is really there.
- A team lead needs evidence of what an engineer can do without help, for onboarding, for a
  promotion case, or after a stretch of heavy AI assistance. CodeTrain records unaided completion
  per step and reports "no data" rather than zero when nothing assessable happened.
- Somebody wants to learn a specific concept by writing it rather than watching it. Name the
  topic and a lesson is written on the spot.
- You want a stepwise lesson generated from any public repository, with secrets and ignored files
  refused rather than read.
- A developer already works in Claude Code, or in OpenCode, and wants a tutor inside it.
  CodeTrain Open Skill, free and open source, installs with
  `npx skills add InferHaven/agent-skills --skill codetrain`: same rule that you write every line,
  no account. See [CodeTrain Open Skill](https://codetrain.ai/docs/open-source-skill/).

Bad fits, and we would rather say so:

- You want the code written. CodeTrain will not do it, by design and with a code-level guard on
  top of the prompt rule. Use a coding assistant.
- You want a video course, a quiz, or a certificate. There are none.
- You want to grade somebody without their knowledge. Every record here is attached to work the
  person did in front of them.

## Which CodeTrain is which?

CodeTrain is one product with one account, and there are two ways in today: the website at codetrain.ai and the CodeTrain CLI on your own machine. CodeTrain Open Skill is a separate, free tool that needs no account.

| | Best for | Who teaches | Where your code goes | Account needed |
| --- | --- | --- | --- | --- |
| CodeTrain website (codetrain.ai) | Learning in your browser, on any topic you name, on any public GitHub repository, or from curated courses. The homepage also runs a real lesson with no account. | CodeTrain's tutor, which writes the lesson. | Python and JavaScript run in your browser; languages a browser cannot run, such as bash, run on CodeTrain's servers. Code you submit, and files you attach, reach CodeTrain's servers and the model provider, and are stored in your lesson. | A CodeTrain account, with a free plan and no card. |
| CodeTrain CLI | Working on the repository in your current folder, or on a practice project, from your own machine. | CodeTrain's tutor, running on your machine and serving its interface on `127.0.0.1`. | Your repository stays on your machine: the CodeTrain CLI reads the checkout in place, and only the prompt snippets needed for one tutoring turn go to the model provider. CodeTrain never copies or stores the repository. Lessons stay in your project folder. | Signs in to your CodeTrain account, and your plan's limits apply. With your own model key in its config file, model calls go straight to your provider. |
| CodeTrain Open Skill | Learning inside the coding agent you already use, such as Claude Code or OpenCode. | Your agent's own model, teaching with CodeTrain's method: you write every line, and it sets the steps, gives hints and reviews your work. | The lesson page runs on `127.0.0.1`. Your agent sends what it reads, your code included, to its own model provider, as it does for any task. Python runs in your browser. | No account, and nothing goes to CodeTrain: no telemetry either. Free and open source, Apache 2.0. |

## How to call CodeTrain

Read this site rather than scraping it:

- Every public page serves markdown. Send `Accept: text/markdown` and you get the page as
  markdown with `Vary: Accept`; ask for a type we cannot serve and you get a 404 or a 406, never
  a 200 carrying the wrong thing.
- `https://codetrain.ai/llms-full.txt` is this entire public site as one markdown file.
- `https://codetrain.ai/sitemap.xml` is the canonical URL list.
- A path that does not exist answers a real 404 with a markdown recovery list, so a 200 from this
  domain always means the page is real.

Call the public API for structured data. No key, no account, base URL `https://api.codetrain.ai`:

```
curl -s https://api.codetrain.ai/v1/catalog
curl -s https://api.codetrain.ai/v1/changelog
curl -s -H "Accept: text/markdown" https://codetrain.ai/learn/
```

Read endpoints allow 120 requests per minute per IP, and how much of that you get
depends on what kind of client you are: 480/min if you sign your requests with HTTP
Message Signatures (RFC 9421, `Signature-Agent` plus a published key directory), 120
if your User-Agent names you, and 30 if neither. Nothing is blocked; the unnamed
budget is simply smaller. Every response carries `RateLimit-Limit`, `RateLimit-Remaining` and
`RateLimit-Reset`, so throttle from those rather than from a 429. A 429 carries `Retry-After`.

What you may do with what you fetch is in https://codetrain.ai/robots.txt as a `Content-Signal` line: search and
AI answers yes, model training no. Security contact: https://codetrain.ai/.well-known/security.txt.

Full reference: https://codetrain.ai/developers/

## Start here

- [AI Coding Tutor That Never Writes Your Code](https://codetrain.ai/): CodeTrain is a Socratic AI coding tutor: it asks questions, reviews what you write, and runs your tests, but never writes the code for you. Free to start.
- [Documentation](https://codetrain.ai/docs/index.md): Every CodeTrain document in one index: how the tutor works, the public developer API, security and privacy, the changelog and the roadmap.
- [The free open-source coding tutor for your coding agent](https://codetrain.ai/docs/open-source-skill/index.md): CodeTrain Open Skill is a free, open-source Agent Skill that runs inside your own coding agent. You write every line; it sets the steps, gives hints and reviews your work. Apache 2.0.
- [Developer API](https://codetrain.ai/developers/index.md): The public CodeTrain REST API: catalog, changelog and roadmap endpoints, no key required, with rate-limit headers, a versioning policy and an OpenAPI document.
- [Learn to code, one small step at a time](https://codetrain.ai/learn/index.md): Every CodeTrain course and class: hands-on lessons where you write every line yourself and the tutor runs it. Python, JavaScript, bash, and how LLMs actually work.

## Courses

- [How a Socratic AI Coding Tutor Works](https://codetrain.ai/learn/socratic-method/index.md): A Socratic coding tutor asks questions instead of writing your code. The exact rules CodeTrain's tutor runs under, quoted from the prompt itself.
- [Learn Any Codebase in 30 Minutes](https://codetrain.ai/learn/understand-a-codebase/index.md): Point an AI tutor at a public repo and learn how it works by writing code in it, not by reading a summary. The thirty minute path, and what it refuses to read.
- [Why AI Coding Assistants Stop You Learning](https://codetrain.ai/learn/why-ai-assistants-stop-you-learning/index.md): An assistant removes the one step that builds the skill. What that costs, when it is still the right tool, and what to use when you want to keep the ability.
- [Learn to Code in Python | Foundations, Collections](https://codetrain.ai/learn/python-intro/index.md): Start from zero and write real Python from your very first line. Hands-on lessons where you write every line yourself and every step has to run.
- [Foundations | Learn to Code in Python](https://codetrain.ai/learn/python-intro/py-foundations/index.md): Variables, functions, and loops: the moves every program is built from. A class in Learn to Code in Python. Free to start, no card.
- [Collections | Learn to Code in Python](https://codetrain.ai/learn/python-intro/py-collections/index.md): Build, filter, and reshape groups of data the Pythonic way. A class in Learn to Code in Python. Free to start, no card.
- [Object-Oriented Python | Classes & objects](https://codetrain.ai/learn/python-oop/index.md): Model real things with classes, and learn when OOP earns its keep. Hands-on lessons where you write every line yourself and every step has to run.
- [Classes & objects | Object-Oriented Python](https://codetrain.ai/learn/python-oop/oop-classes/index.md): Bundle data and behavior together into your own types. A class in Object-Oriented Python. Free to start, no card.
- [JavaScript Fundamentals | Values & arrays](https://codetrain.ai/learn/js-intro/index.md): The language that runs the web: values, arrays, and control flow. Hands-on lessons where you write every line yourself and every step has to run.
- [Values & arrays | JavaScript Fundamentals](https://codetrain.ai/learn/js-intro/js-values/index.md): The data structures you'll touch in every JavaScript program. A class in JavaScript Fundamentals. Free to start, no card.
- [JavaScript: Functions & Data | Functions & closures](https://codetrain.ai/learn/js-functions/index.md): Functions are values: pass them around, return them, and capture state. Hands-on lessons where you write every line yourself and every step has to run.
- [Functions & closures | JavaScript: Functions & Data](https://codetrain.ai/learn/js-functions/jsf-functions/index.md): Higher-order functions and the closures that give them memory. A class in JavaScript: Functions & Data. Free to start, no card.
- [Command the Terminal: Linux & Bash | First commands](https://codetrain.ai/learn/bash-intro/index.md): Stop fearing the shell. Move around, wire commands, automate the boring parts. Hands-on lessons where you write every line yourself and every step has to run.
- [First commands | Command the Terminal: Linux & Bash](https://codetrain.ai/learn/bash-intro/sh-first/index.md): Print, store, loop, and pipe, running live in a real sandbox. A class in Command the Terminal: Linux & Bash. Free to start, no card.
- [Text & pipes | Command the Terminal: Linux & Bash](https://codetrain.ai/learn/bash-intro/sh-text/index.md): Text & pipes, a hands-on class in Command the Terminal: Linux & Bash. A class in Command the Terminal: Linux & Bash. Free to start, no card.
- [How LLMs Actually Work | Neural-net foundations](https://codetrain.ai/learn/llm-foundations/index.md): From a single neuron to a working transformer, built from scratch in pure NumPy, in your browser. Free to start, no card.
- [Neural-net foundations | How LLMs Actually Work](https://codetrain.ai/learn/llm-foundations/llm-foundations-1/index.md): History, a trainable neuron, an N-gram model, and the RNN the transformer replaced. A class in How LLMs Actually Work. Free to start, no card.
- [Tokens & embeddings | How LLMs Actually Work](https://codetrain.ai/learn/llm-foundations/llm-foundations-2/index.md): Turn text into vectors: tokenizers, embeddings, similarity, and position. A class in How LLMs Actually Work. Free to start, no card.
- [The Transformer block | How LLMs Actually Work](https://codetrain.ai/learn/llm-foundations/llm-foundations-3/index.md): Self-attention, causal masking, multi-head, LayerNorm, and the full block. A class in How LLMs Actually Work. Free to start, no card.
- [Training, generation & fine-tuning](https://codetrain.ai/learn/llm-foundations/llm-foundations-4/index.md): Assemble a GPT, learn the loss, sample text, and see how assistants are aligned. A class in How LLMs Actually Work. Free to start, no card.
- [Running LLMs in Production | How LLMs Actually Work](https://codetrain.ai/learn/llm-foundations/running-llms-in-production/index.md): Running LLMs in Production, a hands-on class in How LLMs Actually Work. A class in How LLMs Actually Work. Free to start, no card.

## Comparisons

- [How CodeTrain compares](https://codetrain.ai/compare/index.md): Honest comparisons between CodeTrain and the four categories it gets confused with: general AI study modes, AI coding assistants, coding course platforms, and AI course builders.
- [CodeTrain vs general AI study modes](https://codetrain.ai/compare/ai-study-modes/index.md): Study modes teach Socratically and they are free and good. Where they stop for code specifically, why a learner has to type it, and when not to use us.
- [CodeTrain vs AI coding assistants](https://codetrain.ai/compare/ai-coding-assistants/index.md): Assistants produce code. CodeTrain teaches the engineer to read and change it, with every line typed by the learner. Where each fits, and when not to use us.
- [CodeTrain vs AI onboarding tools](https://codetrain.ai/compare/ai-onboarding-tools/index.md): AI onboarding tools give a new engineer a map of your codebase fast. CodeTrain makes them write code against it, and shows you who can do the work.
- [Copilot or Cursor alternatives for learning to code](https://codetrain.ai/compare/copilot-cursor-alternatives-for-learning/index.md): Use Copilot or Cursor and want to learn the code, not just ship it? From keeping your assistant to tutors built for learning, here are the real options.
- [Best Socratic AI coding tutors compared](https://codetrain.ai/compare/socratic-ai-coding-tutors/index.md): A fair roundup of AI coding tutors that teach with questions: Code.org, Khanmigo, ChatGPT study mode, CodeTeach, KodeKloud and CodeTrain, and who each suits.
- [CodeTrain vs coding course platforms](https://codetrain.ai/compare/coding-course-platforms/index.md): Course platforms teach a fixed curriculum on example projects. CodeTrain teaches on the codebase your team ships. Includes when a course platform wins.
- [CodeTrain vs AI course builders](https://codetrain.ai/compare/ai-course-builders/index.md): AI course builders turn documents into courses. CodeTrain teaches on the codebase itself and verifies the work by running it. Including when not to use us.

## Company and policies

- [Privacy Policy](https://codetrain.ai/privacy): What CodeTrain collects, what it sends to a model provider, and what never leaves your machine. Written for a developer to actually read.
- [Security & Data Handling](https://codetrain.ai/security): Where your code goes, what leaves your machine, what we refuse to read, and what our error monitoring is not allowed to collect. Written for the person who has to sign off on it.
- [Terms of Service](https://codetrain.ai/terms): The terms covering CodeTrain accounts, plans, acceptable use, and what we do and do not promise about AI-generated lesson content.
- [About CodeTrain | Who builds it and why](https://codetrain.ai/about/index.md): CodeTrain is a Socratic AI coding tutor built by InferHaven in Michigan. What the product does, who builds it, and the three things it will not do.
- [Contact CodeTrain | Support, sales and security](https://codetrain.ai/contact/index.md): Reach CodeTrain: the support, sales, security and privacy addresses, what each one is for, and the postal details for CodeTrain by InferHaven in Michigan.

## Optional

- [Learn to Code on Real Codebases | CodeTrain for developers](https://codetrain.ai/solo): A Socratic AI tutor that never writes your code. Pick a course or paste any public repo and CodeTrain builds a hands-on lesson from it. You type every line. Free for ten lessons a month.
- [Roadmap](https://codetrain.ai/roadmap/index.md): What CodeTrain has shipped since launch, what is being built now, and what is under consideration. Dated where it is real, undated where it would be a guess.
- [What CodeTrain runs on](https://codetrain.ai/stack/index.md): The tools CodeTrain is built on, written about by the person who picked them: what each one is for, what it costs, and where it has caught us out.
- [Conductor Network: the CodeTrain affiliate program](https://codetrain.ai/conductors/index.md): Earn 20% of every payment from anyone who joins CodeTrain through your link, every month they keep paying, rising to 25%. 5 Pro referrals cover your own plan.
- [Changelog](https://codetrain.ai/changelog/index.md): Every user-facing change to CodeTrain since launch, newest first. The same release notes shown inside the product.

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