Create an extension
The folder structure and properties an extension needs, from its README and changelog to the actions it exposes.
An extension is a folder with a required shape, and the extensions server picks it up once the shape is right.
What the folder must contain
Folder name
The folder name identifies the extension, so choose it deliberately.
README
Every extension needs a README. For a public extension it becomes the extension's Marketplace page, read by people deciding whether to use the extension.
Write it for them rather than as internal documentation: what the extension does, what it needs configured, and what its actions are.
Changelog
Every extension needs a changelog. See Versioning.
What the extension declares
The extension declares its own metadata, its settings, and the actions it exposes.
Start from the hello-world extension
The repository includes a hello-world extension. Read it before writing a new one; it's faster than working out the shape from documentation.
Next steps
Next: Extension settings, which is what the person installing the extension fills in.