@@ -1,14 +1,11 @@
 const path = require('path');
 const fs = require('fs-extra');
 
-const { listDirectories, listFiles } = require('./utils');
+const { listDirectories, listFiles, signale } = require('./utils');
 const { rootDir } = require('./constants');
-const validate = {
-  js: require('./js'),
-};
+const validators = require('./validators');
 
 const categories = listDirectories(rootDir).filter(dir => dir !== 'node_modules');
-let hasError = false;
 for (const category of categories) {
   const categoryDir = path.resolve(rootDir, category);
   const algorithms = listDirectories(categoryDir);
@@ -17,16 +14,28 @@ for (const category of categories) {
     const files = listFiles(algorithmDir);
     for (const file of files) {
       const ext = file.split('.').pop();
-      const validator = validate[ext];
+      const validator = validators[ext];
       if (validator) {
+        const errors = [];
+        const error = message => errors.push(message);
+        const warns = [];
+        const warn = message => warns.push(message);
         const filePath = path.resolve(algorithmDir, file);
         const content = fs.readFileSync(filePath, 'utf-8');
-        if (!validator(category, algorithm, file, content)) {
-          hasError = true;
-        }
+        validator(error, warn, category, algorithm, file, content)
+          .then(() => {
+            if (errors.length || warns.length) {
+              signale.log(`${category}/${algorithm}/${file}`);
+              errors.forEach(error => signale.error(error));
+              warns.forEach(error => signale.warn(error));
+              signale.log();
+            }
+            if (errors.length) {
+              process.exitCode = 1;
+            }
+          })
+          .catch(console.error);
       }
     }
   }
 }
-
-process.exit(hasError ? 1 : 0);
 
@@ -0,0 +1,25 @@
+const { MAX_STEPS } = require('../constants');
+
+function ensureCodeFoldings(error, warn, content) {
+  if (!/\/\/ import visualization libraries {/.test(content)) {
+    error('Missing the code folding for importing visualization libraries.');
+  }
+  if (!/\/\/ define tracer variables {/.test(content)) {
+    error('Missing the code folding for defining tracer variables.');
+  }
+  if (!/\/\/ visualize {/.test(content)) {
+    error('Missing the code folding for visualizing.');
+  }
+}
+
+function ensureMaxSteps(error, warn, commands) {
+  const steps = commands.filter(command => command.method === 'delay').length;
+  if (steps > MAX_STEPS) {
+    warn('Too many steps.');
+  }
+}
+
+module.exports = {
+  ensureCodeFoldings,
+  ensureMaxSteps,
+};
@@ -0,0 +1,7 @@
+const js = require('./js');
+const java = require('./java');
+
+module.exports = {
+  js,
+  java,
+};
@@ -0,0 +1,18 @@
+const rp = require('request-promise');
+const { ensureMaxSteps, ensureCodeFoldings } = require('./common');
+
+module.exports = async (error, warn, category, algorithm, file, content) => {
+  try {
+    // TODO: Cache the response and restore if sha of the content matches
+    const commands = await rp({
+      method: 'POST',
+      uri: 'https://algorithm-visualizer.org/api/tracers/java',
+      form: { code: content },
+      json: true,
+    });
+    ensureMaxSteps(error, warn, commands);
+  } catch (e) {
+    error(e);
+  }
+  ensureCodeFoldings(error, warn, content);
+};
@@ -0,0 +1,17 @@
+process.env.ALGORITHM_VISUALIZER = '1';
+
+const path = require('path');
+const { ensureMaxSteps, ensureCodeFoldings } = require('./common');
+const { Commander } = require('algorithm-visualizer');
+const { rootDir } = require('../constants');
+
+module.exports = async (error, warn, category, algorithm, file, content) => {
+  try {
+    Commander.init();
+    require(path.resolve(rootDir, category, algorithm, file));
+    ensureMaxSteps(error, warn, Commander.commands);
+  } catch (e) {
+    error(e);
+  }
+  ensureCodeFoldings(error, warn, content);
+};