gatsby-tags.js

const tags = result.data.tagsGroup.group

tags.forEach(tag => {
  createPage({
    path: `/blog/tag:${tag.fieldValue.toLowerCase()}`,
    component: tabPage,
    context: {
      tag: tag.fieldValue,
    },
  })
})

const categories = result.data.categoriesGroup.group

categories.forEach(category => {
  createPage({
    path: `/blog/category:${category.fieldValue.toLowerCase()}`,
    component: categoryPage,
    context: {
      category: category.fieldValue,
    },
  })
})