add rumdl

CLAUDE.md

@@ -0,0 +1,35 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+```bash
+make build   # docker buildx build -t hexletbasics/base-image .
+make push    # docker push hexletbasics/base-image
+```
+
+Validation (used by derived images via `common/common.mk`):
+
+```bash
+make check              # runs all checks: description-lint, schema-validate, test
+make description-lint   # yamllint on module description YAML files
+make schema-validate    # ajv-cli validates spec/language/module/lesson YAML against JSON schemas
+make test               # runs tests in all module Makefiles
+```
+
+## Architecture
+
+This is a Docker base image for HexletBasics's coding exercise platform. Derived images extend it with language-specific runtimes (Python, Ruby, Java, etc.).
+
+**Base image** (`Dockerfile`): built from `node:25-slim`, includes pnpm, python3, git, jq, yamllint, yq, ajv-cli. Published to DockerHub as `hexletbasics/base-image:latest`.
+
+**Multi-arch strategy**: amd64 is built and pushed on every push to `main` (GitHub Actions). arm64 is built nightly on an ARM64 runner. A combined multi-arch manifest is created and pushed as `:latest` after the nightly arm64 build.
+
+**`common/` directory**: copied into derived images at `/opt/basics/common`. Contains:
+- JSON schemas (`spec.json`, `module.json`, `language.json`, `lesson.json`) for validating course content YAML
+- Validation shell scripts in `common/bin/` that call `ajv-cli`
+- `common.mk` — a shared Makefile included by derived image repos to run the full validation chain
+- `yamllint.yml` — shared yamllint config (line-length checks disabled)
+
+Derived image repos include `common.mk` via `include /opt/basics/common/common.mk` and rely on this image being available on DockerHub.

Dockerfile

@@ -5,7 +5,7 @@ ENV LANG=C.UTF-8
 ENV LC_ALL=C.UTF-8
 ENV DEBIAN_FRONTEND=noninteractive
 ENV PNPM_HOME="/pnpm"
-ENV PATH="$PNPM_HOME:$PATH"
+ENV PATH="$PNPM_HOME/bin:$PNPM_HOME:$PATH"
 
 RUN rm -f /etc/apt/apt.conf.d/docker-clean \
   && echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' > /etc/apt/apt.conf.d/keep-cache
@@ -22,4 +22,6 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
 
 RUN pnpm install -g ajv-cli
 
+RUN pip install rumdl --break-system-packages
+
 COPY ./common /opt/basics/common

common/.rumdl.toml

@@ -0,0 +1,3 @@
+# TODO: move to base image
+[global]
+disable = ["MD013", "MD041", "MD033"]

common/common.mk

@@ -1,14 +1,19 @@
 COMMON_DIR := /opt/basics/common
 
-check: description-lint code-lint schema-validate test
+check: description-lint code-lint schema-validate markdown-lint test
 
 description-lint:
 	yamllint modules -c $(COMMON_DIR)/yamllint.yml
 
 test:
 	@(for i in $$(find modules/** -type f -name Makefile); do make test -C $$(dirname $$i) || exit 1; done)
 
-# TODO: add markdown linter and spellckeck (languagetool)
+markdown-lint:
+	rumdl check --config $(COMMON_DIR)/.rumdl.toml modules
+
+markdown-lint-fix:
+	rumdl fmt --config $(COMMON_DIR)/.rumdl.toml modules
+
 schema-validate:
 	@$(COMMON_DIR)/bin/validate-spec.sh
 	@$(COMMON_DIR)/bin/validate-language.sh