diff --git a/src/index.ts b/src/index.ts
index 6c1b5ce..fff528e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import peg from 'pegjs';
 import { MfmNode } from './node';
+import { stringifyNode, stringifyTree } from './util';
 const parser: peg.Parser = require('./parser');
 
 export function parse(input: string): MfmNode[] {
@@ -12,95 +13,14 @@ export function parsePlain(input: string): MfmNode[] {
 	return nodes;
 }
 
-function nodeStringify(node: MfmNode): string {
-	switch(node.type) {
-		// block
-		case 'quote': {
-			return toString(node.children).split('\n').map(line => `>${line}`).join('\n');
-		}
-		case 'search': {
-			return node.props.content;
-		}
-		case 'blockCode': {
-			return `\`\`\`${ node.props.lang ?? '' }\n${ node.props.code }\n\`\`\``;
-		}
-		case 'mathBlock': {
-			return `\\[\n${ node.props.formula }\n\\]`;
-		}
-		case 'center': {
-			return `<center>${ toString(node.children) }</center>`;
-		}
-		// inline
-		case 'emoji': {
-			if (node.props.name) {
-				return `:${ node.props.name }:`;
-			}
-			else if (node.props.emoji) {
-				return node.props.emoji;
-			}
-			else {
-				return '';
-			}
-		}
-		case 'bold': {
-			return `**${ toString(node.children) }**`;
-		}
-		case 'small': {
-			return `<small>${ toString(node.children) }</small>`;
-		}
-		case 'italic': {
-			return `<i>${ toString(node.children) }</i>`;
-		}
-		case 'strike': {
-			return `~~${ toString(node.children) }~~`;
-		}
-		case 'inlineCode': {
-			return `\`${ node.props.code }\``;
-		}
-		case 'mathInline': {
-			return `\\(${ node.props.formula }\\)`;
-		}
-		case 'mention': {
-			return node.props.acct;
-		}
-		case 'hashtag': {
-			return `#${ node.props.hashtag }`;
-		}
-		case 'url': {
-			return node.props.url;
-		}
-		case 'link': {
-			const prefix = node.props.silent ? '?' : '';
-			return `${ prefix }[${ toString(node.children) }](${ node.props.url })`;
-		}
-		case 'fn': {
-			const argFields = Object.keys(node.props.args).map(key => {
-				const value = node.props.args[key];
-				if (value === true) {
-					return key;
-				}
-				else {
-					return `${ key }=${ value }`;
-				}
-			});
-			const args = (argFields.length > 0) ? '.' + argFields.join(',') : '';
-			return `[${ node.props.name }${ args } ${ toString(node.children) }]`;
-		}
-		case 'text': {
-			return node.props.text;
-		}
-	}
-	throw new Error('unknown mfm node');
-}
-
-export function toString(nodes: MfmNode[]): string
+export function toString(tree: MfmNode[]): string
 export function toString(node: MfmNode): string
 export function toString(node: MfmNode | MfmNode[]): string {
 	if (Array.isArray(node)) {
-		return node.map(n => nodeStringify(n)).join('');
+		return stringifyTree(node);
 	}
 	else {
-		return nodeStringify(node);
+		return stringifyNode(node);
 	}
 }
 
diff --git a/src/util.ts b/src/util.ts
index 58a4a6c..8b96d18 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -71,6 +71,91 @@ export function mergeText(trees: MfmNode[] | undefined, recursive?: boolean): Mf
 	}
 }
 
+export function stringifyNode(node: MfmNode): string {
+	switch(node.type) {
+		// block
+		case 'quote': {
+			return stringifyTree(node.children).split('\n').map(line => `>${line}`).join('\n');
+		}
+		case 'search': {
+			return node.props.content;
+		}
+		case 'blockCode': {
+			return `\`\`\`${ node.props.lang ?? '' }\n${ node.props.code }\n\`\`\``;
+		}
+		case 'mathBlock': {
+			return `\\[\n${ node.props.formula }\n\\]`;
+		}
+		case 'center': {
+			return `<center>${ stringifyTree(node.children) }</center>`;
+		}
+		// inline
+		case 'emoji': {
+			if (node.props.name) {
+				return `:${ node.props.name }:`;
+			}
+			else if (node.props.emoji) {
+				return node.props.emoji;
+			}
+			else {
+				return '';
+			}
+		}
+		case 'bold': {
+			return `**${ stringifyTree(node.children) }**`;
+		}
+		case 'small': {
+			return `<small>${ stringifyTree(node.children) }</small>`;
+		}
+		case 'italic': {
+			return `<i>${ stringifyTree(node.children) }</i>`;
+		}
+		case 'strike': {
+			return `~~${ stringifyTree(node.children) }~~`;
+		}
+		case 'inlineCode': {
+			return `\`${ node.props.code }\``;
+		}
+		case 'mathInline': {
+			return `\\(${ node.props.formula }\\)`;
+		}
+		case 'mention': {
+			return node.props.acct;
+		}
+		case 'hashtag': {
+			return `#${ node.props.hashtag }`;
+		}
+		case 'url': {
+			return node.props.url;
+		}
+		case 'link': {
+			const prefix = node.props.silent ? '?' : '';
+			return `${ prefix }[${ stringifyTree(node.children) }](${ node.props.url })`;
+		}
+		case 'fn': {
+			const argFields = Object.keys(node.props.args).map(key => {
+				const value = node.props.args[key];
+				if (value === true) {
+					return key;
+				}
+				else {
+					return `${ key }=${ value }`;
+				}
+			});
+			const args = (argFields.length > 0) ? '.' + argFields.join(',') : '';
+			return `[${ node.props.name }${ args } ${ stringifyTree(node.children) }]`;
+		}
+		case 'text': {
+			return node.props.text;
+		}
+	}
+	throw new Error('unknown mfm node');
+}
+
+export function stringifyTree(tree: MfmNode[]): string {
+	return tree.map(n => stringifyNode(n)).join('');
+}
+
 //
 // dynamic consuming
 //