Make SEO score in Lighthouse = 100

For meta description used `excerpt` as it's close enough and doesn't require adding an extra frontmatter field.

src/pages/index.js

@@ -10,11 +10,19 @@ import { rhythm } from '../utils/typography'
 class BlogIndex extends React.Component {
   render() {
     const siteTitle = get(this, 'props.data.site.siteMetadata.title')
+    const siteDescription = get(
+      this,
+      'props.data.site.siteMetadata.description'
+    )
     const posts = get(this, 'props.data.allMarkdownRemark.edges')
 
     return (
       <Layout location={this.props.location}>
-        <Helmet title={siteTitle} htmlAttributes={{ lang: 'en' }} />
+        <Helmet
+          htmlAttributes={{ lang: 'en' }}
+          meta={[{ name: 'description', content: siteDescription }]}
+          title={siteTitle}
+        />
         <Bio />
         {posts.map(({ node }) => {
           const title = get(node, 'frontmatter.title') || node.fields.slug
@@ -46,6 +54,7 @@ export const pageQuery = graphql`
     site {
       siteMetadata {
         title
+        description
       }
     }
     allMarkdownRemark(sort: { fields: [frontmatter___date], order: DESC }) {

src/templates/blog-post.js

@@ -11,13 +11,15 @@ class BlogPostTemplate extends React.Component {
   render() {
     const post = this.props.data.markdownRemark
     const siteTitle = get(this.props, 'data.site.siteMetadata.title')
+    const siteDescription = post.excerpt
     const { previous, next } = this.props.pageContext
 
     return (
       <Layout location={this.props.location}>
         <Helmet
-          title={`${post.frontmatter.title} | ${siteTitle}`}
           htmlAttributes={{ lang: 'en' }}
+          meta={[{ name: 'description', content: siteDescription }]}
+          title={`${post.frontmatter.title} | ${siteTitle}`}
         />
         <h1>{post.frontmatter.title}</h1>
         <p
@@ -80,6 +82,7 @@ export const pageQuery = graphql`
     }
     markdownRemark(fields: { slug: { eq: $slug } }) {
       id
+      excerpt
       html
       frontmatter {
         title