Vercel build: JavaScript heap out of memory since I added 300 blog posts

Raising the heap only moves the wall. Two better levers:

1. Don't prebuild everything. Return only recent/popular posts from generateStaticParams, the rest render on first request and get cached:

export const dynamicParams = true; // default, but be explicit

export async function generateStaticParams() {
  const posts = await getPosts();
  return posts.slice(0, 50).map((p) => ({ slug: p.slug }));
}

2. Check what each page loads. If every post page imports a helper that reads all 300 MDX files (for "related posts" or the sidebar), you parse 300 × 300 files. Build the index once into a small JSON and read that.

In your case I'd bet on #2, memory growing linearly with post count usually means that.