Configure Netlify builds and routing via netlify.toml, _redirects, and _headers. Use when setting a build command or publish directory, adding redirects or rewrites or proxies, adding an SPA fallback rewrite, setting custom response headers or basic auth, managing environment variables and secrets, scoping vars per deploy context, marking a var as secret, disabling secret scanning, configuring functions bundling, ignoring builds, or wiring up a monorepo or JavaScript SPA on Netlify.