diff --git a/client/homebrew/editor/metadataEditor/metadataEditor.jsx b/client/homebrew/editor/metadataEditor/metadataEditor.jsx
index 25b4daac8..b5f9ddc25 100644
--- a/client/homebrew/editor/metadataEditor/metadataEditor.jsx
+++ b/client/homebrew/editor/metadataEditor/metadataEditor.jsx
@@ -9,6 +9,7 @@ const Nav = require('naturalcrit/nav/nav.jsx');
 const StringArrayEditor = require('../stringArrayEditor/stringArrayEditor.jsx');
 
 const Themes = require('themes/themes.json');
+const validations = require('./validations.js')
 
 const SYSTEMS = ['5e', '4e', '3.5e', 'Pathfinder'];
 
@@ -22,6 +23,7 @@ const MetadataEditor = createClass({
 				editId      : null,
 				title       : '',
 				description : '',
+				thumbnail   : '',
 				tags        : [],
 				published   : false,
 				authors     : [],
@@ -51,11 +53,30 @@ const MetadataEditor = createClass({
 	},
 
 	handleFieldChange : function(name, e){
-		this.props.onChange({
-			...this.props.metadata,
-			[name] : e.target.value
-		});
+		e.persist();
+
+		// load validation rules, and check input value against them
+		const inputRules = validations[name] ?? [];
+		const validationErr = inputRules.map((rule)=>rule(e.target.value)).filter(Boolean);
+
+		// if no validation rules, save to props
+		if(validationErr.length === 0){
+			e.target.setCustomValidity('');
+			this.props.onChange({
+				...this.props.metadata,
+				[name] : e.target.value
+			});
+		} else {
+			// if validation issues, display built-in browser error popup with each error.
+			console.log(validationErr);
+			const errMessage = validationErr.map((err)=>{
+				return `- ${err}`;
+			}).join('\n');
+			e.target.setCustomValidity(errMessage);
+			e.target.reportValidity();
+		};
 	},
+
 	handleSystem : function(system, e){
 		if(e.target.checked){
 			this.props.metadata.systems.push(system);
@@ -64,6 +85,7 @@ const MetadataEditor = createClass({
 		}
 		this.props.onChange(this.props.metadata);
 	},
+
 	handleRenderer : function(renderer, e){
 		if(e.target.checked){
 			this.props.metadata.renderer = renderer;
@@ -228,21 +250,21 @@ const MetadataEditor = createClass({
 			<div className='field title'>
 				<label>title</label>
 				<input type='text' className='value'
-					value={this.props.metadata.title}
+					defaultValue={this.props.metadata.title}
 					onChange={(e)=>this.handleFieldChange('title', e)} />
 			</div>
 			<div className='field-group'>
 				<div className='field-column'>
 					<div className='field description'>
 						<label>description</label>
-						<textarea value={this.props.metadata.description} className='value'
+						<textarea defaultValue={this.props.metadata.description} className='value'
 							onChange={(e)=>this.handleFieldChange('description', e)} />
 					</div>
 					<div className='field thumbnail'>
 						<label>thumbnail</label>
 						<input type='text'
-							value={this.props.metadata.thumbnail}
-							placeholder='my.thumbnail.url'
+							defaultValue={this.props.metadata.thumbnail}
+							placeholder='https://my.thumbnail.url'
 							className='value'
 							onChange={(e)=>this.handleFieldChange('thumbnail', e)} />
 						<button className='display' onClick={this.toggleThumbnailDisplay}>
diff --git a/client/homebrew/editor/metadataEditor/metadataEditor.less b/client/homebrew/editor/metadataEditor/metadataEditor.less
index 9b2761306..f0974fb6c 100644
--- a/client/homebrew/editor/metadataEditor/metadataEditor.less
+++ b/client/homebrew/editor/metadataEditor/metadataEditor.less
@@ -42,6 +42,12 @@
 		&>.value{
 			flex           : 1 1 auto;
 			width          : 50px;
+			&:invalid {
+				background : #ffb9b9;
+			}
+		}
+		input[type='text'], textarea {
+			border : 1px solid gray;
 		}
 		&.thumbnail{
 			height      : 1.4em;
diff --git a/client/homebrew/editor/metadataEditor/validations.js b/client/homebrew/editor/metadataEditor/validations.js
new file mode 100644
index 000000000..22f9e918b
--- /dev/null
+++ b/client/homebrew/editor/metadataEditor/validations.js
@@ -0,0 +1,34 @@
+module.exports = {
+	title : [
+		(value)=>{
+			return value?.length > 100 ? 'Max title length of 100 characters' : null;
+		}
+	],
+	description : [
+		(value)=>{
+			return value?.length > 500 ? 'Max description length of 500 characters.' : null;
+		}
+	],
+	thumbnail : [
+		(value)=>{
+			return value?.length > 256 ? 'Max URL length of 256 characters.' : null;
+		},
+		(value)=>{
+			if(value?.length == 0){return null;}
+			try {
+				Boolean(new URL(value));
+				return null;
+			} catch (e) {
+				return 'Must be a valid URL';
+			}
+		}
+	],
+	language : [
+		(value)=>{
+			return new RegExp(/[a-z]{2,3}(-.*)?/).test(value || '') === false ? 'Invalid language code.' : null;
+		}
+	]
+};
+
+
+