This article provides a step by step guide to publishing one markdown article to dev.to, Medium, AWS Builder Center and LinkedIn with publishing-kit, an agent skill for Claude Code, Codex and Antigravity. The article you are reading was published with it, and every command output below comes from that run.
One markdown file goes in. A dev.to draft, a Medium story, a Builder Center draft and a LinkedIn post come out, each one checked before it ships.
Markdown is the easy part. You write headings, a table, a few code blocks and a cover image, and it looks right in your editor and on GitHub.
| Destination | Publishing API | Tables | Multi-line code | Cover | | :--- | :--- | :--- | :--- | :--- | | dev.to | 🟢 full REST API | 🟢 native | 🟢 native | URL, cropped to 2.381:1 | | Medium | ❌ unsupported since 2023 | ❌ dropped | ❌ one line | first image in the body | | AWS Builder Center | ❌ none | 🟢 native | 🟢 line-numbered | 1200x675 upload | | LinkedIn | ⚠️ posts only, no drafts | ❌ none | ❌ none | link card or upload |
Every one of those differences fails without an error. You get a plausible-looking page with a missing table, a code block run together on one line, or a cover with its title cut off, and you see it after it is live.
The importer (medium.com/p/import) brings in prose, headings, links and images from a URL. It drops markdown tables entirely, flattens blocks to a single line, strips HTML comments, and renders only two heading sizes, so ## sections all read as titles. A link inside an image caption makes the whole image disappear. It also caches by URL and ignores the query string, so re-importing a fixed page with ?v=2 brings back the old one.
Pasting into the editor keeps multi-line code, but removes any image embedded as a data: URI, with no placeholder left behind.
The API would avoid all of this, and Medium's own documentation now opens with "The Medium API is no longer supported. We do not recommend using it." The repository was archived in 2023.
So Medium can only be reached by driving its editor in a browser, with its quirks known in advance.
dev.to has a complete REST API: create, update, list, and route to an organization. It renders markdown with hard line breaks on, so a source file wrapped at 80 columns publishes with a break in the middle of every paragraph. It displays the cover through a 2.381:1 crop, which cuts the top and bottom off a 16:9 image. And an update through the API sends the front matter's published: false along with the body, which takes a live article back to draft.
AWS Builder Center has no publishing API. The body goes in by pasting into a browser editor, and its publish step checks every link, including URLs written as plain text, and refuses with a message that names none of them.
LinkedIn has a Posts API, but PUBLISHED is the only state it accepts on creation, so anything posted through it goes straight to your feed. The post text renders no markdown at all.
It packages the workarounds as an agent skill plus a set of small Python scripts. The skill tells the agent what each destination needs; the scripts do the parts that should be exact. One source, four artifacts. The dev.to markdown is the source. make-medium.py renders tables to images and writes Medium HTML, make-builder.py writes the Builder Center version, make-linkedin.py writes the post. Covers at the size that is shown. make-cover.py draws one design at every geometry the destinations need and names each file by a hash of its bytes. A pre-flight that fails the build. preflight.py checks the cover, the front matter, the prose, the links and every number in the article, and exits non-zero. The API where one exists. publish-devto.py posts to dev.to with no browser. Browser helpers where none does. Small in-page scripts for the Medium and Builder Center editors that refuse to act when something looks wrong.
At This Point You Should Have… Claude Code, Codex or Antigravity, with browser automation for the Medium and Builder Center steps. Python 3 with Pillow, and pandoc for the Medium build. A public GitHub repository for the article's directory. Covers and Medium images are fetched by URL, so they must be pushed before you publish. A dev.to API key in ~/.devto.key or $DEVTOAPI_KEY. Signed-in browser sessions for Medium, Builder Center and LinkedIn.
Most of the time you do not run the scripts yourself. You ask the agent to publish, and it runs them.
The source is a dev.to markdown file with front matter, because dev.to renders tables, code and emoji natively. Everything else is derived from it. This is the front matter of this article:
published: false stays in the file. Going live is a separate command, so a routine update never publishes by accident.
The prompt that started this article was one sentence: "write another article that explains what this skill does, step through how to use it and publish it, and dogfood the article with the kit."