diff --git a/.idea/libraries/dist.xml b/.idea/libraries/dist.xml
new file mode 100644
index 0000000..3d92275
--- /dev/null
+++ b/.idea/libraries/dist.xml
@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="dist" type="javaScript">
+    <properties>
+      <sourceFilesUrls>
+        <item url="file://$PROJECT_DIR$/dist" />
+      </sourceFilesUrls>
+    </properties>
+    <CLASSES>
+      <root url="file://$PROJECT_DIR$/dist" />
+    </CLASSES>
+    <SOURCES />
+  </library>
+</component>
\ No newline at end of file
diff --git a/src/routes/template.spec.ts b/src/routes/template.spec.ts
index 68b99e9..c2e6fcd 100644
--- a/src/routes/template.spec.ts
+++ b/src/routes/template.spec.ts
@@ -4,7 +4,6 @@ import TemplateTreatmentModel from '../models/treatment_template';
 import TemplateMeasurementModel from '../models/measurement_template';
 import TestHelper from "../test/helper";
 
-// TODO: check number prefix to have no numbers
 
 describe('/template', () => {
   let server;
@@ -371,14 +370,14 @@ describe('/template', () => {
           res: {status: 'Invalid body format', details: '"parameters[0].name" is required'}
         });
       });
-      it('rejects a missing number prefix', done => {
+      it('rejects a number prefix containing numbers', done => {
         TestHelper.request(server, done, {
           method: 'post',
           url: '/template/treatment/new',
           auth: {basic: 'admin'},
           httpStatus: 400,
-          req: {name: 'heat aging', parameters: [{name: 'time', range: {min: 1}}]},
-          res: {status: 'Invalid body format', details: '"number_prefix" is required'}
+          req: {name: 'heat aging', number_prefix: 'AB5', parameters: [{name: 'time', range: {min: 1}}]},
+          res: {status: 'Invalid body format', details: '"number_prefix" with value "AB5" fails to match the required pattern: /^[a-zA-Z]+$/'}
         });
       });
       it('rejects a missing parameter range', done => {
diff --git a/src/routes/validate/template.ts b/src/routes/validate/template.ts
index 7cb461d..269e1a2 100644
--- a/src/routes/validate/template.ts
+++ b/src/routes/validate/template.ts
@@ -1,35 +1,36 @@
-import joi from '@hapi/joi';
+import Joi from '@hapi/joi';
 import IdValidate from './id';
 
 export default class TemplateValidate {
   private static template = {
-    name: joi.string()
+    name: Joi.string()
       .max(128),
 
-    version: joi.number()
+    version: Joi.number()
       .min(1),
 
-    number_prefix: joi.string()
+    number_prefix: Joi.string()
+      .pattern(/^[a-zA-Z]+$/)
       .min(1)
       .max(16),
 
-    parameters: joi.array()
+    parameters: Joi.array()
       .min(1)
       .items(
-        joi.object({
-          name: joi.string()
+        Joi.object({
+          name: Joi.string()
             .max(128)
             .required(),
 
-          range: joi.object({
-            values: joi.array()
+          range: Joi.object({
+            values: Joi.array()
               .min(1),
 
-            min: joi.number(),
+            min: Joi.number(),
 
-            max: joi.number(),
+            max: Joi.number(),
 
-            type: joi.string()
+            type: Joi.string()
               .valid('array')
           })
             .oxor('values', 'min')
@@ -45,14 +46,14 @@ export default class TemplateValidate {
   static input (data, param, template) {  // validate data, param: new(everything required)/change(available attributes are validated)
     if (param === 'new') {
       if (template === 'treatment') {
-        return joi.object({
+        return Joi.object({
           name: this.template.name.required(),
           number_prefix: this.template.number_prefix.required(),
           parameters: this.template.parameters.required()
         }).validate(data);
       }
       else {
-        return joi.object({
+        return Joi.object({
           name: this.template.name.required(),
           parameters: this.template.parameters.required()
         }).validate(data);
@@ -60,14 +61,14 @@ export default class TemplateValidate {
     }
     else if (param === 'change') {
       if (template === 'treatment') {
-        return joi.object({
+        return Joi.object({
           name: this.template.name,
           number_prefix: this.template.number_prefix,
           parameters: this.template.parameters
         }).validate(data);
       }
       else {
-        return joi.object({
+        return Joi.object({
           name: this.template.name,
           parameters: this.template.parameters
         }).validate(data);
@@ -98,7 +99,7 @@ export default class TemplateValidate {
         parameters: this.template.parameters
       };
     }
-    const {value, error} = joi.object(joiObject).validate(data, {stripUnknown: true});
+    const {value, error} = Joi.object(joiObject).validate(data, {stripUnknown: true});
     return error !== undefined? null : value;
   }
 }
\ No newline at end of file