Support TOML format in frontmatter and block props

[caelyreth]

Description

Add support for TOML as an alternative format for document frontmatter and component block props, alongside the existing YAML support.

This would allow authors to use either format interchangeably (or mix them across files/components) without changing Comark’s core data model.

Motivation

Many users (myself included) come from ecosystems where TOML is a first-class citizen for configuration and frontmatter — most notably Hugo, which has long supported TOML via the +++ delimiter.

TOML offers several practical advantages for content authors:

• It is largely indentation-insensitive, reducing friction when editing nested structures.
• Nested tables and arrays are explicit and readable without relying on significant whitespace.
• It is already widely used in modern tooling (Cargo, pyproject.toml, many static-site generators, etc.), so the mental model is familiar to a large group of developers.

Supporting TOML as a complementary format would lower the barrier for users migrating from Hugo or other TOML-centric workflows, while keeping YAML as the default for those who prefer it.

Proposed solution

I propose adding TOML support as a sibling path to the existing YAML handling:

1. Use the lightweight, well-maintained smol-toml package.
2. Follow the established community convention of +++ (as used by Hugo and others).

Example frontmatter:

+++
date = 2024-02-02T04:14:54-08:00
draft = false
title = "Example"
weight = 10

[params]
author = "John Smith"
+++

If the you are open to this feature, I’m happy to open a PR that implements TOML parsing as a parallel path next to the existing YAML implementation.

Alternatives considered

No response

Additional context

No response

[atinux]

Hi @caelyreth and thanks for the feedback!

Comark work with a plugins system, I believe this should be easily achievable by creating a frontmatter-toml plugin, see for instance the frontmatter plugin: https://github.com/comarkdown/comark/blob/main/packages/comark/src/plugins/frontmatter.ts

We have a plugin template if you are interested to try building your own: https://github.com/comarkdown/comark-plugin-template

Then testing it with:

import { parseMarkdown } from 'comark'
import frontmatterToml from 'comark-frontmatter-toml'

const result = await parseMarkdown(content, {
  registerDefaultPlugins: false,
  plugins: [frontmatterToml()],
})

Learn more in https://comark.dev/plugins#default-plugins-disable-default-plugins

[caelyreth]

Thanks for the idea from @atinux!

I’m going to try using the plugin system to implement this soon. If it works, I’ll close this issue. Otherwise, I’ll follow up with your team to provide feedback.

[atinux]

Thank you @caelyreth, if your plugin works well, we are happy to link to it as alternative of YAML for frontmatter :)

[caelyreth]

Thanks for the guidance, @atinux!

I've implemented this as a plugin at comark-toml (also available on npm as comark-toml).

It adds support for both frontmatter and block props; the usage is straightforward:

import { parseMarkdown } from 'comark'
import toml from 'comark-toml'

const document = await parseMarkdown(content, { plugins: [toml()] })

It is compatible with the default plugins, the behaviors are documented here.

I've used this in my private web project, it works fine and has no visible issues.

Happy to close this issue now that the plugin exists.

Feel free to link it as an alternative for TOML frontmatter/block props if it looks good.