diff --git a/.github/workflows/test-activerecord.yml b/.github/workflows/test-activerecord.yml
index edd83f7..0002661 100644
--- a/.github/workflows/test-activerecord.yml
+++ b/.github/workflows/test-activerecord.yml
@@ -1,6 +1,6 @@
 ---
 name: test-activerecord
-on: [push, pull_request]
+on: workflow_call
 permissions:
   contents: read
 jobs:
@@ -10,12 +10,12 @@ jobs:
       fail-fast: false
       matrix:
         entry:
-          - { ruby: '3.3', activerecord: '~> 6.1.0', grape: '~> 1.8', rack: '~> 2.2' }
-          - { ruby: '3.3', activerecord: '~> 7.2.0', grape: '~> 2.4' }
-          - { ruby: '3.3', activerecord: '~> 7.2.0', grape: '~> 3.0' }
-          - { ruby: '3.4', activerecord: '~> 8.0.0', grape: '~> 2.4' }
-          - { ruby: '3.4', activerecord: '~> 8.1.0', grape: '~> 4.0' }
-          - { ruby: '4.0', activerecord: '~> 8.1.0', grape: '~> 4.0' }
+          - { ruby: '3.3', activerecord: '~> 6.1.0', grape: '~> 1.8', rack: '~> 2.2', coverage: false }
+          - { ruby: '3.3', activerecord: '~> 7.2.0', grape: '~> 2.4', coverage: false }
+          - { ruby: '3.3', activerecord: '~> 7.2.0', grape: '~> 3.0', coverage: true }
+          - { ruby: '3.4', activerecord: '~> 8.0.0', grape: '~> 2.4', coverage: false }
+          - { ruby: '3.4', activerecord: '~> 8.1.0', grape: '~> 4.0', coverage: false }
+          - { ruby: '4.0', activerecord: '~> 8.1.0', grape: '~> 4.0', coverage: false }
     name: test (ruby=${{ matrix.entry.ruby }}, activerecord=${{ matrix.entry.activerecord }}, grape=${{ matrix.entry.grape }})
     env:
       ACTIVERECORD_VERSION: ${{ matrix.entry.activerecord }}
@@ -29,3 +29,11 @@ jobs:
           bundler-cache: true
       - name: Run Tests
         run: bundle exec rake spec
+      - uses: coverallsapp/github-action@v2
+        if: matrix.entry.coverage
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          file: coverage/lcov/grape-roar.lcov
+          format: lcov
+          flag-name: activerecord-${{ strategy.job-index }}
+          parallel: true
diff --git a/.github/workflows/test-mongodb.yml b/.github/workflows/test-mongodb.yml
index 473c2cc..fc623f1 100644
--- a/.github/workflows/test-mongodb.yml
+++ b/.github/workflows/test-mongodb.yml
@@ -1,6 +1,6 @@
 ---
 name: test-mongodb
-on: [push, pull_request]
+on: workflow_call
 permissions:
   contents: read
 jobs:
@@ -10,13 +10,13 @@ jobs:
       fail-fast: false
       matrix:
         entry:
-          - { ruby: '3.3', mongoid: '~> 6.4.8', mongodb: '6.0', grape: '~> 1.7.0', rack: '~> 2.2' }
-          - { ruby: '3.3', mongoid: '~> 6.4.8', mongodb: '6.0', grape: '~> 2.0.0' }
-          - { ruby: '3.3', mongoid: '~> 7.5.4', mongodb: '7.0', grape: '~> 2.4' }
-          - { ruby: '3.3', mongoid: '~> 8.1.11', mongodb: '8.0', grape: '~> 2.4' }
-          - { ruby: '3.3', mongoid: '~> 8.1.11', mongodb: '8.0', grape: '~> 3.0' }
-          - { ruby: '3.4', mongoid: '~> 9.1', mongodb: '8.0', grape: '~> 4.0' }
-          - { ruby: '4.0', mongoid: '~> 9.1', mongodb: '8.0', grape: '~> 4.0' }
+          - { ruby: '3.3', mongoid: '~> 6.4.8', mongodb: '6.0', grape: '~> 1.7.0', rack: '~> 2.2', coverage: false }
+          - { ruby: '3.3', mongoid: '~> 6.4.8', mongodb: '6.0', grape: '~> 2.0.0', coverage: true }
+          - { ruby: '3.3', mongoid: '~> 7.5.4', mongodb: '7.0', grape: '~> 2.4', coverage: false }
+          - { ruby: '3.3', mongoid: '~> 8.1.11', mongodb: '8.0', grape: '~> 2.4', coverage: false }
+          - { ruby: '3.3', mongoid: '~> 8.1.11', mongodb: '8.0', grape: '~> 3.0', coverage: false }
+          - { ruby: '3.4', mongoid: '~> 9.1', mongodb: '8.0', grape: '~> 4.0', coverage: true }
+          - { ruby: '4.0', mongoid: '~> 9.1', mongodb: '8.0', grape: '~> 4.0', coverage: false }
     name: test (ruby=${{ matrix.entry.ruby }}, mongoid=${{ matrix.entry.mongoid }}, mongodb=${{ matrix.entry.mongodb }}, grape=${{ matrix.entry.grape }})
     env:
       MONGOID_VERSION: ${{ matrix.entry.mongoid }}
@@ -40,3 +40,11 @@ jobs:
           bundler-cache: true
       - name: Run Tests
         run: bundle exec rake spec
+      - uses: coverallsapp/github-action@v2
+        if: matrix.entry.coverage
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          file: coverage/lcov/grape-roar.lcov
+          format: lcov
+          flag-name: mongoid-${{ strategy.job-index }}
+          parallel: true
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 19bd011..6d6c6d6 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -32,3 +32,16 @@ jobs:
           bundler-cache: true
       - name: Run Tests
         run: bundle exec rake spec
+  test-activerecord:
+    uses: ./.github/workflows/test-activerecord.yml
+  test-mongodb:
+    uses: ./.github/workflows/test-mongodb.yml
+  finish:
+    name: Finish Coveralls
+    needs: [test, test-activerecord, test-mongodb]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: coverallsapp/github-action@v2
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          parallel-finished: true
diff --git a/.gitignore b/.gitignore
index d5a4807..ff97a2f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,4 +2,5 @@ Gemfile.lock
 doc
 pkg
 .bundle
+/coverage/
 gemfiles/*.lock
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index dfd6cce..86e43bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * [#40](https://github.com/ruby-grape/grape-roar/pull/40): Document deeply nested representers and verify shared post/image records retain their attributes across repeated requests - [@dblock](https://github.com/dblock).
 * [#42](https://github.com/ruby-grape/grape-roar/pull/42): Support caching plain rendered representations without forwarding Roar-only options to generic JSON encoders; document cache serialization and request-context keys - [@dblock](https://github.com/dblock).
 * [#41](https://github.com/ruby-grape/grape-roar/pull/41): Document hash-backed representers with explicit key getters and verify module/decorator rendering for symbol and string keys - [@dblock](https://github.com/dblock).
+* [#43](https://github.com/ruby-grape/grape-roar/pull/43): Add SimpleCov LCOV reports and a coverage badge; merge Coveralls reports from selected existing ORM matrix entries without duplicate test runs - [@dblock](https://github.com/dblock).
 * Your contribution here.
 
 ### 0.5.0 (2025/09/25)
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a641c27..f47fdd6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -50,6 +50,8 @@ GRAPE_VERSION='~> 1.8' RACK_VERSION='~> 2.2' bundle exec rake
 
 Setting `ACTIVERECORD_VERSION` or `MONGOID_VERSION` loads that ORM and automatically includes its tagged examples in the suite. ActiveRecord adapter and validation tests do not require a database. Mongoid examples require MongoDB at `localhost:27017` and use the dedicated `grape_roar_test` database. CI runs MongoDB service containers for Mongoid 6.x through 9.x and tests newer Grape versions with ORM releases that permit their ActiveSupport requirements.
 
+Spec runs generate `coverage/lcov/grape-roar.lcov` with SimpleCov. `test.yml` runs the core matrix and calls the separate reusable `test-activerecord.yml` and `test-mongodb.yml` workflows. Only `test.yml` handles push and pull-request events, so the ORM matrices run once per event. ORM entries marked `coverage: true` upload reports using the built-in GitHub token, covering ActiveRecord and both Mongoid association implementations without extra test runs. After the core matrix and both reusable workflows succeed, one completion job in `test.yml` merges the uploads into a single Coveralls report.
+
 #### Write Tests
 
 Try to write a test that reproduces the problem you're trying to fix or describes a feature that you want to build. Add to [spec/grape-roar](spec/grape-roar).
diff --git a/Gemfile b/Gemfile
index 0e9aa0a..451f1ac 100644
--- a/Gemfile
+++ b/Gemfile
@@ -12,6 +12,8 @@ gemspec
 group :test do
   gem 'rack-test'
   gem 'rspec'
+  gem 'simplecov', require: false
+  gem 'simplecov-lcov', require: false
 end
 
 group :development, :test do
diff --git a/README.md b/README.md
index aa3fc5f..75cc131 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,8 @@ Grape::Roar
 -----------
 
 [![Gem Version](http://img.shields.io/gem/v/grape-roar.svg)](http://badge.fury.io/rb/grape-roar)
+[![Coverage Status](https://coveralls.io/repos/github/ruby-grape/grape-roar/badge.svg?branch=master)](https://coveralls.io/github/ruby-grape/grape-roar?branch=master)
 [![test](https://github.com/ruby-grape/grape-roar/actions/workflows/test.yml/badge.svg)](https://github.com/ruby-grape/grape-roar/actions/workflows/test.yml)
-[![test-activerecord](https://github.com/ruby-grape/grape-roar/actions/workflows/test-activerecord.yml/badge.svg)](https://github.com/ruby-grape/grape-roar/actions/workflows/test-activerecord.yml)
-[![test-mongodb](https://github.com/ruby-grape/grape-roar/actions/workflows/test-mongodb.yml/badge.svg)](https://github.com/ruby-grape/grape-roar/actions/workflows/test-mongodb.yml)
 
 Use [Roar](https://github.com/apotonick/roar) with [Grape](https://github.com/intridea/grape).
 
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 0983ce2..57d5554 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -10,6 +10,16 @@
 
 require 'bundler'
 Bundler.setup :default, :test
+
+require 'simplecov'
+require 'simplecov-lcov'
+SimpleCov::Formatter::LcovFormatter.config.report_with_single_file = true
+SimpleCov::Formatter::LcovFormatter.config.lcov_file_name = 'grape-roar.lcov'
+SimpleCov.formatter = SimpleCov::Formatter::LcovFormatter
+SimpleCov.start do
+  add_filter '/spec/'
+end
+
 Bundler.require
 
 require 'grape'