diff --git a/src/polysolve/nonlinear/Criteria.cpp b/src/polysolve/nonlinear/Criteria.cpp
index 3dd6e11..23e771f 100644
--- a/src/polysolve/nonlinear/Criteria.cpp
+++ b/src/polysolve/nonlinear/Criteria.cpp
@@ -18,6 +18,8 @@ namespace polysolve::nonlinear
 
     void Criteria::reset()
     {
+        constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
+
         iterations = 0;
         xDelta = 0;
         fDelta = 0;
@@ -25,13 +27,18 @@ namespace polysolve::nonlinear
         firstGradNorm = 0;
         fDeltaCount = 0;
         xDeltaDotGrad = 0;
+
+        energy = NaN;
+        alpha = NaN;
+        step = NaN;
     }
 
     void Criteria::print(std::ostream &os) const
     {
         os << print_message();
     }
-    std::string Criteria::print_message() const {
+    std::string Criteria::print_message() const
+    {
         return fmt::format(
             "iters={:d} Δf={:g} ‖∇f‖={:g} ‖Δx‖={:g} Δx⋅∇f(x)={:g}",
             iterations, fDelta, gradNorm, xDelta, xDeltaDotGrad);
@@ -64,7 +71,8 @@ namespace polysolve::nonlinear
         return Status::Continue;
     }
 
-    std::string_view status_message(Status s) {
+    std::string_view status_message(Status s)
+    {
         switch (s)
         {
         case Status::NotStarted:
diff --git a/src/polysolve/nonlinear/Criteria.hpp b/src/polysolve/nonlinear/Criteria.hpp
index d4e770c..6140714 100644
--- a/src/polysolve/nonlinear/Criteria.hpp
+++ b/src/polysolve/nonlinear/Criteria.hpp
@@ -39,6 +39,9 @@ namespace polysolve::nonlinear
         double xDeltaDotGrad; ///< Dot product of parameter vector and gradient vector
         unsigned fDeltaCount; ///< Number of steps where fDelta is satisfied
 
+        double alpha;  ///< LS alpha
+        double energy; ///< Energy at the current step
+        double step;   ///< alpha * grad.norm()
         Criteria();
 
         void reset();
@@ -50,7 +53,7 @@ namespace polysolve::nonlinear
     Status checkConvergence(const Criteria &stop, const Criteria &current);
 
     std::string_view status_message(Status s);
-    std::string criteria_message(const Criteria& s);
+    std::string criteria_message(const Criteria &s);
 
     std::ostream &operator<<(std::ostream &os, const Status &s);
 
diff --git a/src/polysolve/nonlinear/Solver.cpp b/src/polysolve/nonlinear/Solver.cpp
index 1b98faa..799d4d9 100644
--- a/src/polysolve/nonlinear/Solver.cpp
+++ b/src/polysolve/nonlinear/Solver.cpp
@@ -299,6 +299,7 @@ namespace polysolve::nonlinear
                 POLYSOLVE_SCOPED_STOPWATCH("compute objective function", obj_fun_time, m_logger);
                 energy = objFunc(x);
             }
+            m_current.energy = energy;
 
             if (!std::isfinite(energy))
             {
@@ -413,6 +414,7 @@ namespace polysolve::nonlinear
                 POLYSOLVE_SCOPED_STOPWATCH("line search", line_search_time, m_logger);
                 rate = m_line_search->line_search(x, delta_x, objFunc);
             }
+            m_current.alpha = rate;
 
             if (std::isnan(rate))
             {
@@ -466,6 +468,7 @@ namespace polysolve::nonlinear
             // Post update
             // -----------
             const double step = (rate * delta_x).norm();
+            m_current.step = step;
 
             // m_logger.debug("[{}][{}] rate={:g} ‖step‖={:g}",
             //                descent_strategy_name(), m_line_search->name(), rate, step);
@@ -481,6 +484,12 @@ namespace polysolve::nonlinear
 
             m_current.fDeltaCount = (m_current.fDelta < m_stop.fDelta) ? (m_current.fDeltaCount + 1) : 0;
 
+            if (m_iteration_callback && m_iteration_callback(m_current))
+            {
+                m_status = Status::ObjectiveCustomStop;
+                m_logger.debug("[{}][{}] Iteration callback decided to stop", descent_strategy_name(), m_line_search->name());
+            }
+
             m_logger.debug(
                 "[{}][{}] {} (stopping criteria: {})",
                 descent_strategy_name(), m_line_search->name(), m_current.print_message(), m_stop.print_message());
diff --git a/src/polysolve/nonlinear/Solver.hpp b/src/polysolve/nonlinear/Solver.hpp
index 211ea98..9f291d0 100644
--- a/src/polysolve/nonlinear/Solver.hpp
+++ b/src/polysolve/nonlinear/Solver.hpp
@@ -79,15 +79,16 @@ namespace polysolve::nonlinear
         void set_line_search(const json &params);
         const json &info() const { return solver_info; }
 
+        void set_iteration_callback(std::function<bool(const Criteria &)> callback) { m_iteration_callback = callback; }
+
         /// @brief If true the solver will not throw an error if the maximum number of iterations is reached
         bool allow_out_of_iterations = false;
 
-
         /// @brief Get the line search object
         const std::shared_ptr<line_search::LineSearch> &line_search() const { return m_line_search; };
 
     protected:
-        /// @brief Compute direction in which the argument should be updated 
+        /// @brief Compute direction in which the argument should be updated
         /// @param objFunc Problem to be minimized
         /// @param x Current input (n x 1)
         /// @param grad Gradient at current step (n x 1)
@@ -106,8 +107,8 @@ namespace polysolve::nonlinear
         Criteria m_stop;
 
         /// @brief Current criteria
-        Criteria m_current;
 
+        Criteria m_current;
         /// @brief Current status
         Status m_status = Status::NotStarted;
 
@@ -139,7 +140,7 @@ namespace polysolve::nonlinear
         // ====================================================================
         //                           Solver state
         // ====================================================================
-        
+
         /// @brief Reset the solver at the start of a minimization
         /// @param ndof number of degrees of freedom
         void reset(const int ndof);
@@ -151,12 +152,14 @@ namespace polysolve::nonlinear
 
         std::vector<int> m_iter_per_strategy;
 
+        std::function<bool(const Criteria &)> m_iteration_callback = nullptr;
+
         // ====================================================================
         //                            Solver info
         // ====================================================================
 
         /// @brief Update solver info JSON object
-        /// @param energy 
+        /// @param energy
         void update_solver_info(const double energy);
 
         /// @brief Reset timing members to 0