How to implement SEO in a Reactjs application?

Implementing SEO in a React.js application can be slightly more difficult than in a traditional HTML/CSS/JavaScript site, mostly because React is a JavaScript library that loads content dynamically. Search engines sometimes have a hard time crawling and indexing these kind of sites.

Here are some strategies and tools to help you with SEO in your React applications:

1. Use of meta tags: Meta tags give search engines guidance and context about your page. Libraries such as React Helmet are great for working with metadata in a React application.

```
import { Helmet } from ‘react-helmet’;

function MyComponent() { return (

My Title

);
}
```

1. Server-side Rendering (SSR): When your website is requested, the server sends a fully rendered page to the client for the first hit. This significantly improves the SEO performance because search engine crawlers can read the initial page load. Popular frameworks for SSR with React include Next.js and Gatsby.

1. Pre-rendering: This is a simpler solution compared to SSR, where you run a “headless” browser in your build process that navigates to every route, then save the resulting HTML and send that when users visit your site. Services like Prerender.io can help you do this, or if you want a DIY solution, Puppeteer is a popular library for pre-rendering.

1. Use Canonical URLs: These tags tell search engines which is the primary page you want to index, in the case of duplicate pages. You may need these especially if you are using react-router’s dynamic routing. You can use the ‘react-helmet’ library to add a canonical tag to your pages.

1. SiteMap & Robots.txt: Create a sitemap of your application and a robots.txt file to guide the crawler.

1. Use of structured data: This is code in a specific format, written in such a way that search engines understand it. Search engines read the code and use it to display search results in a specific and much richer way. You can use JSON-LD for this.

1. Accessibility: A well-structured, semantic HTML markup helps search engines understand your site better, improving your SEO.

1. Use of hyphen instead of underscores in URLs: According to Google, hyphens are easier to interpret for search bots than underscores.

1. Social Share Metadata: To customize how your web page content appears in social shares, use Open Graph protocol and Twitter Cards.

To test what a crawler might see when it requests your page, you can use tools such as Google’s Mobile-Friendly Test or Fetch as Google. To see what a fully rendered page might look like, you can use pre-rendering services like BromBone or Prerender.io.

Proper SEO involves a lot more. However, these are some specific points to be followed when using React.js.

You can use tools like Moz SEO, Google Search Console, Google Lighthouse, Alexa etc., to analyze and improvise the SEO of your React application.

Also, using Next.js for React applications can enhance SEO. It provides features like static exporting, pre-rendering and server-side rendering which can help ensure that all of your content is fully crawled and indexed.