diff --git a/server/package.json b/server/package.json
index 230811b45..2a4ca2256 100644
--- a/server/package.json
+++ b/server/package.json
@@ -9,6 +9,11 @@
     "start": "nodemon --exec babel-node --presets env,stage-2 src/index.js",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
+  "standard": {
+    "ignore": [
+      "/src/errors/index.js"
+    ]
+  },
   "devDependencies": {
     "babel-cli": "^6.26.0",
     "babel-preset-env": "^1.7.0",
diff --git a/server/src/errors/index.js b/server/src/errors/index.js
index eb000c4ee..cfb70457e 100644
--- a/server/src/errors/index.js
+++ b/server/src/errors/index.js
@@ -1,4 +1,14 @@
 export class AuthentificationError extends Error {
   code = 401
-  message = 'You have to be authentificated to ' + ( this.message || "perform this action")
+  message = 'Autentification not found, you have to be authentificated to perform this action'
+}
+
+export class DatabaseError extends Error {
+  code = 404
+  message = 'Ressource not found : ' + this.message
+}
+
+export class WrongArgumentsError extends Error {
+  code = 400
+  message = 'Wrong arguments : ' + this.message
 }
diff --git a/server/src/schema/mutations/AddPrize.js b/server/src/schema/mutations/AddPrize.js
index 620442ab6..03e79b7c4 100644
--- a/server/src/schema/mutations/AddPrize.js
+++ b/server/src/schema/mutations/AddPrize.js
@@ -3,7 +3,11 @@ import {
   GraphQLID,
   GraphQLInt
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import {
+  AuthentificationError,
+  DatabaseError,
+  WrongArgumentsError
+} from '../../errors'
 import { EventType } from '../types'
 import { Event } from '../../models'
 
@@ -20,12 +24,13 @@ const resolve = (parent, { eventDesignator, rank, amount }, context) => {
   }
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         if (event.prizes.some(prize => prize.rank === rank)) {
-          // need to add an error message here TODO
-          resolve(event)
+          reject(new WrongArgumentsError('A prize for that rank already exists'))
         } else {
           event.prizes.push({
             rank,
diff --git a/server/src/schema/mutations/AddRule.js b/server/src/schema/mutations/AddRule.js
index b3183fb6c..6968ab4e9 100644
--- a/server/src/schema/mutations/AddRule.js
+++ b/server/src/schema/mutations/AddRule.js
@@ -3,7 +3,11 @@ import {
   GraphQLID,
   GraphQLString
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import {
+  AuthentificationError,
+  DatabaseError,
+  WrongArgumentsError
+} from '../../errors'
 import { EventType } from '../types'
 import { Event } from '../../models'
 
@@ -20,11 +24,13 @@ const resolve = (parent, { eventDesignator, title, description }, context) => {
   }
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         if (event.rules.some(rule => rule.title === title)) {
-          resolve(event)
+          reject(new WrongArgumentsError('A prize for that rank already exists'))
         } else {
           let position = 1
           while (event.rules.some(rule => rule.position === position)) {
diff --git a/server/src/schema/mutations/CreateAndSetFormula.js b/server/src/schema/mutations/CreateAndSetFormula.js
index f8e145a22..21f631a1b 100644
--- a/server/src/schema/mutations/CreateAndSetFormula.js
+++ b/server/src/schema/mutations/CreateAndSetFormula.js
@@ -2,7 +2,7 @@ import {
   GraphQLNonNull,
   GraphQLString
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import { AuthentificationError, DatabaseError } from '../../errors'
 import { EventType } from '../types'
 import { Event, Formula } from '../../models'
 
@@ -19,8 +19,10 @@ const resolve = (parent, { name, eventDesignator }, context) => {
   let newFormula = new Formula({ name, ownerId })
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId: ownerId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         newFormula.save((err) => {
           if (err) reject(err)
diff --git a/server/src/schema/mutations/CreateAndSetPlotter.js b/server/src/schema/mutations/CreateAndSetPlotter.js
index 75d518614..98aa2e7e4 100644
--- a/server/src/schema/mutations/CreateAndSetPlotter.js
+++ b/server/src/schema/mutations/CreateAndSetPlotter.js
@@ -2,7 +2,7 @@ import {
   GraphQLNonNull,
   GraphQLString
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import { AuthentificationError, DatabaseError } from '../../errors'
 import { EventType } from '../types'
 import { Event, Plotter } from '../../models'
 
@@ -22,8 +22,10 @@ const resolve = (parent, { name, host, repo, moduleName, eventDesignator }, cont
   let newPlotter = new Plotter({ name, host, repo, moduleName, ownerId })
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId: ownerId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         newPlotter.save((err) => {
           if (err) reject(err)
diff --git a/server/src/schema/mutations/EditEvent.js b/server/src/schema/mutations/EditEvent.js
index f36fa26f9..de5271efb 100644
--- a/server/src/schema/mutations/EditEvent.js
+++ b/server/src/schema/mutations/EditEvent.js
@@ -4,7 +4,7 @@ import {
   GraphQLInt,
   GraphQLString
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import { AuthentificationError, DatabaseError } from '../../errors'
 import { EventType } from '../types'
 import { Event } from '../../models'
 
@@ -25,8 +25,10 @@ const resolve = (parent, { designator, name, description, startDatetime, finishD
   }
   return new Promise((resolve, reject) => {
     Event.findOne({ designator, hostId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         event.name = name || event.name
         event.description = description || event.description
diff --git a/server/src/schema/mutations/EditRule.js b/server/src/schema/mutations/EditRule.js
index 1821d8aeb..5b3113edf 100644
--- a/server/src/schema/mutations/EditRule.js
+++ b/server/src/schema/mutations/EditRule.js
@@ -3,7 +3,7 @@ import {
   GraphQLID,
   GraphQLString
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import { AuthentificationError, DatabaseError } from '../../errors'
 import { EventType } from '../types'
 import { Event } from '../../models'
 
@@ -21,8 +21,10 @@ const resolve = (parent, { eventDesignator, title, newtitle, description }, cont
   }
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         let ruleIndex
         event.rules.find((rule, index) => {
diff --git a/server/src/schema/mutations/ReorderRules.js b/server/src/schema/mutations/ReorderRules.js
index 00846507e..0a29865d4 100644
--- a/server/src/schema/mutations/ReorderRules.js
+++ b/server/src/schema/mutations/ReorderRules.js
@@ -3,7 +3,7 @@ import {
   GraphQLID,
   GraphQLInt
 } from 'graphql'
-import { AuthentificationError } from '../../errors'
+import { AuthentificationError, DatabaseError } from '../../errors'
 import { isBetween } from '../../utils/functions'
 import { EventType } from '../types'
 import { Event } from '../../models'
@@ -21,8 +21,10 @@ const resolve = (parent, { eventDesignator, fromPosition, toPosition }, context)
   }
   return new Promise((resolve, reject) => {
     Event.findOne({ designator: eventDesignator, hostId: context.userId }).exec((err, event) => {
-      if (err || !event) {
+      if (err) {
         reject(err)
+      } else if (!event) {
+        reject(new DatabaseError('None of the events you own respond to that designator'))
       } else {
         const delta = fromPosition > toPosition ? 1 : -1
         event.rules.forEach((part) => {