diff --git a/CHANGELOG b/CHANGELOG
index e2553bc145c..b7e85f2e5e9 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -13,6 +13,7 @@ v 7.7.0
   - Set project path instead of project name in create form
   -
   -
+  - Updates to the messages returned by API (sponsored by O'Reilly Media)
   - New UI layout with side navigation
   -
   -
diff --git a/lib/api/branches.rb b/lib/api/branches.rb
index 6ec1a753a69..b52d786e020 100644
--- a/lib/api/branches.rb
+++ b/lib/api/branches.rb
@@ -14,7 +14,8 @@ module API
       # Example Request:
       #   GET /projects/:id/repository/branches
       get ":id/repository/branches" do
-        present user_project.repository.branches.sort_by(&:name), with: Entities::RepoObject, project: user_project
+        branches = user_project.repository.branches.sort_by(&:name)
+        present branches, with: Entities::RepoObject, project: user_project
       end
 
       # Get a single branch
@@ -26,7 +27,7 @@ module API
       #   GET /projects/:id/repository/branches/:branch
       get ':id/repository/branches/:branch', requirements: { branch: /.*/ } do
         @branch = user_project.repository.branches.find { |item| item.name == params[:branch] }
-        not_found!("Branch does not exist") if @branch.nil?
+        not_found!("Branch") unless @branch
         present @branch, with: Entities::RepoObject, project: user_project
       end
 
@@ -43,7 +44,7 @@ module API
         authorize_admin_project
 
         @branch = user_project.repository.find_branch(params[:branch])
-        not_found! unless @branch
+        not_found!("Branch") unless @branch
         protected_branch = user_project.protected_branches.find_by(name: @branch.name)
         user_project.protected_branches.create(name: @branch.name) unless protected_branch
 
@@ -63,7 +64,7 @@ module API
         authorize_admin_project
 
         @branch = user_project.repository.find_branch(params[:branch])
-        not_found! unless @branch
+        not_found!("Branch does not exist") unless @branch
         protected_branch = user_project.protected_branches.find_by(name: @branch.name)
         protected_branch.destroy if protected_branch
 
diff --git a/lib/api/commits.rb b/lib/api/commits.rb
index 6c5391b98c8..0de4e720ffe 100644
--- a/lib/api/commits.rb
+++ b/lib/api/commits.rb
@@ -108,7 +108,7 @@ module API
         if note.save
           present note, with: Entities::CommitNote
         else
-          not_found!
+          render_api_error!("Failed to save note #{note.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/files.rb b/lib/api/files.rb
index 84e1d311781..e6e71bac367 100644
--- a/lib/api/files.rb
+++ b/lib/api/files.rb
@@ -35,7 +35,7 @@ module API
         file_path = attrs.delete(:file_path)
 
         commit = user_project.repository.commit(ref)
-        not_found! "Commit" unless commit
+        not_found! 'Commit' unless commit
 
         blob = user_project.repository.blob_at(commit.sha, file_path)
 
@@ -53,7 +53,7 @@ module API
             commit_id: commit.id,
           }
         else
-          render_api_error!('File not found', 404)
+          not_found! 'File'
         end
       end
 
diff --git a/lib/api/groups.rb b/lib/api/groups.rb
index a2d915a7eca..bda60b3b7d5 100644
--- a/lib/api/groups.rb
+++ b/lib/api/groups.rb
@@ -54,7 +54,7 @@ module API
         if @group.save
           present @group, with: Entities::Group
         else
-          not_found!
+          render_api_error!("Failed to save group #{@group.errors.messages}", 400)
         end
       end
 
@@ -97,7 +97,7 @@ module API
         if result
           present group
         else
-          not_found!
+          render_api_error!("Failed to transfer project #{project.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/helpers.rb b/lib/api/helpers.rb
index 2f2342840fd..62c26ef76ce 100644
--- a/lib/api/helpers.rb
+++ b/lib/api/helpers.rb
@@ -42,7 +42,7 @@ module API
 
     def user_project
       @project ||= find_project(params[:id])
-      @project || not_found!
+      @project || not_found!("Project")
     end
 
     def find_project(id)
diff --git a/lib/api/merge_requests.rb b/lib/api/merge_requests.rb
index a365f1db00f..81038d05f12 100644
--- a/lib/api/merge_requests.rb
+++ b/lib/api/merge_requests.rb
@@ -233,7 +233,7 @@ module API
         if note.save
           present note, with: Entities::MRNote
         else
-          render_validation_error!(note)
+          render_api_error!("Failed to save note #{note.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/milestones.rb b/lib/api/milestones.rb
index a4fdb752d69..2ea49359df0 100644
--- a/lib/api/milestones.rb
+++ b/lib/api/milestones.rb
@@ -48,7 +48,7 @@ module API
         if milestone.valid?
           present milestone, with: Entities::Milestone
         else
-          not_found!
+          render_api_error!("Failed to create milestone #{milestone.errors.messages}", 400)
         end
       end
 
@@ -72,7 +72,7 @@ module API
         if milestone.valid?
           present milestone, with: Entities::Milestone
         else
-          not_found!
+          render_api_error!("Failed to update milestone #{milestone.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/notes.rb b/lib/api/notes.rb
index b29c054a044..3726be7c537 100644
--- a/lib/api/notes.rb
+++ b/lib/api/notes.rb
@@ -61,7 +61,7 @@ module API
           if @note.valid?
             present @note, with: Entities::Note
           else
-            not_found!
+            not_found!("Note #{@note.errors.messages}")
           end
         end
 
@@ -93,7 +93,7 @@ module API
           if @note.valid?
             present @note, with: Entities::Note
           else
-            bad_request!('Invalid note')
+            render_api_error!("Failed to save note #{note.errors.messages}", 400)
           end
         end
 
diff --git a/lib/api/project_hooks.rb b/lib/api/project_hooks.rb
index 7d056b9bf58..be9850367b9 100644
--- a/lib/api/project_hooks.rb
+++ b/lib/api/project_hooks.rb
@@ -53,7 +53,7 @@ module API
           if @hook.errors[:url].present?
             error!("Invalid url given", 422)
           end
-          not_found!
+          not_found!("Project hook #{@hook.errors.messages}")
         end
       end
 
@@ -82,7 +82,7 @@ module API
           if @hook.errors[:url].present?
             error!("Invalid url given", 422)
           end
-          not_found!
+          not_found!("Project hook #{@hook.errors.messages}")
         end
       end
 
diff --git a/lib/api/project_members.rb b/lib/api/project_members.rb
index 1595ed0bc36..8e32f124ea5 100644
--- a/lib/api/project_members.rb
+++ b/lib/api/project_members.rb
@@ -9,7 +9,7 @@ module API
           if errors[:access_level].any?
             error!(errors[:access_level], 422)
           end
-          not_found!
+          not_found!(errors)
         end
       end
 
diff --git a/lib/api/projects.rb b/lib/api/projects.rb
index d6dd03656a6..e1cc2348865 100644
--- a/lib/api/projects.rb
+++ b/lib/api/projects.rb
@@ -227,7 +227,7 @@ module API
             render_api_error!("Project already forked", 409)
           end
         else
-          not_found!
+          not_found!("Source Project")
         end
 
       end
diff --git a/lib/api/repositories.rb b/lib/api/repositories.rb
index a1a7721b288..03a556a2c55 100644
--- a/lib/api/repositories.rb
+++ b/lib/api/repositories.rb
@@ -133,7 +133,7 @@ module API
           env['api.format'] = :binary
           present data
         else
-          not_found!
+          not_found!('File')
         end
       end
 
diff --git a/spec/requests/api/fork_spec.rb b/spec/requests/api/fork_spec.rb
index cbbd1e7de5a..5921b3e0698 100644
--- a/spec/requests/api/fork_spec.rb
+++ b/spec/requests/api/fork_spec.rb
@@ -44,7 +44,7 @@ describe API::API, api: true  do
       it 'should fail on missing project access for the project to fork' do
         post api("/projects/fork/#{project.id}", user3)
         response.status.should == 404
-        json_response['message'].should == '404 Not Found'
+        json_response['message'].should == '404 Project Not Found'
       end
 
       it 'should fail if forked project exists in the user namespace' do
@@ -58,7 +58,7 @@ describe API::API, api: true  do
       it 'should fail if project to fork from does not exist' do
         post api('/projects/fork/424242', user)
         response.status.should == 404
-        json_response['message'].should == '404 Not Found'
+        json_response['message'].should == '404 Project Not Found'
       end
     end
 
diff --git a/spec/requests/api/groups_spec.rb b/spec/requests/api/groups_spec.rb
index 8dfd2cd650e..95f82463367 100644
--- a/spec/requests/api/groups_spec.rb
+++ b/spec/requests/api/groups_spec.rb
@@ -91,7 +91,8 @@ describe API::API, api: true  do
 
       it "should not create group, duplicate" do
         post api("/groups", admin), {name: "Duplicate Test", path: group2.path}
-        response.status.should == 404
+        response.status.should == 400
+        response.message.should == "Bad Request"
       end
 
       it "should return 400 bad request error if name not given" do
diff --git a/spec/requests/api/projects_spec.rb b/spec/requests/api/projects_spec.rb
index f8c5d40b9bf..79865f15f06 100644
--- a/spec/requests/api/projects_spec.rb
+++ b/spec/requests/api/projects_spec.rb
@@ -289,7 +289,7 @@ describe API::API, api: true  do
     it "should return a 404 error if not found" do
       get api("/projects/42", user)
       response.status.should == 404
-      json_response['message'].should == '404 Not Found'
+      json_response['message'].should == '404 Project Not Found'
     end
 
     it "should return a 404 error if user is not a member" do
@@ -340,7 +340,7 @@ describe API::API, api: true  do
     it "should return a 404 error if not found" do
       get api("/projects/42/events", user)
       response.status.should == 404
-      json_response['message'].should == '404 Not Found'
+      json_response['message'].should == '404 Project Not Found'
     end
 
     it "should return a 404 error if user is not a member" do