diff --git a/packages/@vuepress/core/lib/dev.js b/packages/@vuepress/core/lib/dev.js
index 2f6e7cddee..2b373cc068 100644
--- a/packages/@vuepress/core/lib/dev.js
+++ b/packages/@vuepress/core/lib/dev.js
@@ -79,6 +79,17 @@ module.exports = async function dev (sourceDir, cliOptions = {}) {
   const port = await resolvePort(cliOptions.port || ctx.siteConfig.port)
   const { host, displayHost } = await resolveHost(cliOptions.host || ctx.siteConfig.host)
 
+  // debug in a running dev process.
+  process.stdout.on('data', chunk => {
+    const parsed = chunk.toString('utf-8').trim()
+    if (parsed === '*') {
+      console.log(Object.keys(ctx))
+    }
+    if (ctx[parsed]) {
+      console.log(ctx[parsed])
+    }
+  })
+
   config
     .plugin('vuepress-log')
     .use(DevLogPlugin, [{