diff --git a/src/jres_solver_base.cpp b/src/jres_solver_base.cpp
index bff1044..af98cc3 100644
--- a/src/jres_solver_base.cpp
+++ b/src/jres_solver_base.cpp
@@ -4,12 +4,20 @@
  * @brief Base class for the JRES Solver.
  */
 #include "jres_solver_base.hpp"
+#include <set>
+#include <stdexcept>
 
 JresSolverBase::JresSolverBase(const jres::internal::SolverInput& input, const JresSolverOptions& options)
     : m_input(input), m_options(options)
 {
     // Filter Participant Pools
+    std::set<std::string> seenNames;
     for (const auto& member : m_input.teamMembers) {
+        if (seenNames.count(member.name)) {
+            throw std::runtime_error("Duplicate team member name: " + member.name);
+        }
+        seenNames.insert(member.name);
+
         if (member.isDriver) m_driverPool.push_back(member);
         if (member.isSpotter) m_spotterPool.push_back(member);
     }
diff --git a/src/jres_standard_solver.cpp b/src/jres_standard_solver.cpp
index 1f98c94..1863e2a 100644
--- a/src/jres_standard_solver.cpp
+++ b/src/jres_standard_solver.cpp
@@ -14,6 +14,7 @@
 #include <sstream>
 #include <iostream>
 #include <iomanip>
+#include <set>
 
 #include "Highs.h"
 
@@ -143,6 +144,16 @@ jres::internal::SolverOutput JresStandardSolver::solve()
     output.config.maximumBusyHours = m_input.maximumBusyHours;
     output.config.firstStintDriver = m_input.firstStintDriver;
 
+    // --- Duplicate Name Check ---
+    std::set<std::string> namesSeen;
+    for (const auto& m : m_input.teamMembers) {
+        if (namesSeen.count(m.name)) {
+            std::string err = "Duplicate team member name: " + m.name;
+            throw std::runtime_error(err);
+        }
+        namesSeen.insert(m.name);
+    }
+
     // --- Arithmetic Pre-flight Check ---
     int totalStints = (int)m_input.stints.size();
     auto capAnalysis = jres::internal::CapacityAnalyzer::calculate_max_potential_capacity(m_driverPool, m_input);
@@ -557,6 +568,18 @@ jres::internal::SolverOutput JresStandardSolver::solve()
         }
     } 
     
+    // --- Final Validation ---
+    for (size_t s = 0; s < output.schedule.size(); ++s) {
+        if (output.schedule[s].driver == "N/A") {
+             output.diagnosis.push_back("Stint " + std::to_string(s) + " (" + output.schedule[s].startTime + ") has no assigned driver.");
+        }
+        
+        bool spotterRequired = (m_options.spotterMode != JRES_SPOTTER_MODE_NONE && !m_options.allowNoSpotter);
+        if (spotterRequired && output.schedule[s].spotter == "N/A") {
+             output.diagnosis.push_back("Stint " + std::to_string(s) + " (" + output.schedule[s].startTime + ") has no assigned spotter.");
+        }
+    }
+
     output.teamMembers = m_input.teamMembers;
     return output;
 }
\ No newline at end of file
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index abdd119..d928c0b 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -41,6 +41,7 @@ add_executable(solver_tests
   test_max_busy_defaults.cpp
   test_availability_overlap.cpp
   test_availability_boundaries.cpp
+  test_validation.cpp
 )
 
 add_dependencies(solver_tests jres_solver_lib)
diff --git a/test/test_validation.cpp b/test/test_validation.cpp
new file mode 100644
index 0000000..52b495e
--- /dev/null
+++ b/test/test_validation.cpp
@@ -0,0 +1,78 @@
+#include "gtest/gtest.h"
+#include "jres_solver/jres_solver.hpp"
+#include <string>
+
+namespace {
+
+    const char* DUPLICATE_NAMES_JSON = R"({
+      "teamMembers": [ 
+          { "name": "DriverA", "isDriver": true },
+          { "name": "DriverA", "isDriver": true }
+      ],
+      "availability": {},
+      "stints": [ { "id": 1, "startTime": "2024-01-01T12:00:00.000Z", "endTime": "2024-01-01T13:00:00.000Z" } ]
+    })";
+
+    TEST(ValidationTest, DuplicateNames) {
+        JresSolverOptions options = {};
+        options.spotterMode = JRES_SPOTTER_MODE_NONE;
+        
+        JresSolverInput* input = jres_input_from_json(DUPLICATE_NAMES_JSON);
+        ASSERT_NE(input, nullptr);
+
+        JresSolverOutput* output = solve_race_schedule(input, &options);
+        ASSERT_NE(output, nullptr);
+
+        // Expect diagnosis
+        ASSERT_GT(output->diagnosis_len, 0);
+        bool foundDuplicateMsg = false;
+        for (int i = 0; i < output->diagnosis_len; ++i) {
+            std::string msg = output->diagnosis[i];
+            if (msg.find("Duplicate team member name") != std::string::npos) {
+                foundDuplicateMsg = true;
+                break;
+            }
+        }
+        EXPECT_TRUE(foundDuplicateMsg) << "Should diagnose duplicate names";
+
+        free_jres_solver_input(input);
+        free_jres_solver_output(output);
+    }
+
+    const char* NO_SPOTTERS_SEQUENTIAL_JSON = R"({
+      "teamMembers": [ 
+          { "name": "DriverA", "isDriver": true, "isSpotter": false },
+          { "name": "SpotterA", "isDriver": false, "isSpotter": false }
+      ],
+      "availability": {},
+      "stints": [ { "id": 1, "startTime": "2024-01-01T12:00:00.000Z", "endTime": "2024-01-01T13:00:00.000Z" } ]
+    })";
+
+    TEST(ValidationTest, UnassignedSpotterSequential) {
+        JresSolverOptions options = {};
+        options.spotterMode = JRES_SPOTTER_MODE_SEQUENTIAL;
+        options.allowNoSpotter = false;
+        
+        JresSolverInput* input = jres_input_from_json(NO_SPOTTERS_SEQUENTIAL_JSON);
+        ASSERT_NE(input, nullptr);
+
+        JresSolverOutput* output = solve_race_schedule(input, &options);
+        ASSERT_NE(output, nullptr);
+
+        // Expect diagnosis about unassigned spotter
+        ASSERT_GT(output->diagnosis_len, 0);
+        bool foundSpecificMsg = false;
+        for (int i = 0; i < output->diagnosis_len; ++i) {
+            std::string msg = output->diagnosis[i];
+            if (msg.find("Stint 0") != std::string::npos && msg.find("has no assigned spotter") != std::string::npos) {
+                foundSpecificMsg = true;
+                break;
+            }
+        }
+
+        EXPECT_TRUE(foundSpecificMsg) << "Should diagnose specific unassigned stint for spotter";
+
+        free_jres_solver_input(input);
+        free_jres_solver_output(output);
+    }
+}