diff --git a/CMakeLists.txt b/CMakeLists.txt
index 90f9cd1..9080f6b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -241,6 +241,7 @@ add_executable(udpscope
   src/source/registry.cpp
   src/source/udps_source.cpp
   src/source/udps_kind.cpp
+  src/source/probe_source.cpp
   src/plot_host.cpp
   src/export.cpp
   src/search.cpp
diff --git a/src/layout_store.cpp b/src/layout_store.cpp
index 857cfb9..0b42d37 100644
--- a/src/layout_store.cpp
+++ b/src/layout_store.cpp
@@ -322,6 +322,10 @@ std::vector<KnownSource> known_sources() {
       s.capture_packets = st.capture_packets;
       s.multicast = st.multicast;
       s.interface_addr = st.interface_addr;
+      if (!st.source_kind.empty()) {
+        s.kind = st.source_kind;
+        s.opts = st.source_opts;
+      }
       s.rows = static_cast<int>(st.rows.size());
       for (const LayoutState::Row& row : st.rows) {
         for (const std::string& sig : row.signals) {
@@ -558,6 +562,11 @@ bool load_layout(const std::string& path, LayoutState& out) {
         st.multicast = strip_quote(value);
       } else if (key == "interface") {
         st.interface_addr = strip_quote(value);
+      } else if (key == "source_kind") {
+        st.source_kind = strip_quote(value);
+      } else if (key.rfind("source_opt_", 0) == 0) {
+        const std::string k = key.substr(11);
+        if (SourceConfig::valid_key(k)) st.source_opts.set(k, strip_quote(value));
       } else if (key == "comment") {
         st.comment = strip_quote(value);
       } else if (key == "buffer_mb") {
@@ -699,6 +708,12 @@ bool save_layout(const std::string& path, const LayoutState& state) {
   if (!state.interface_addr.empty()) {
     o << "interface = " << toml_escape(state.interface_addr) << "\n";
   }
+  if (!state.source_kind.empty() && state.source_kind != "udps") {
+    o << "source_kind = " << toml_escape(state.source_kind) << "\n";
+    for (const auto& kv : state.source_opts.items()) {
+      o << "source_opt_" << kv.first << " = " << toml_escape(kv.second) << "\n";
+    }
+  }
   // Top level, before any table. Emitted after the `[[calibration]]` tables it belonged to the last
   // of them -- a bare key after a header is that table's key in TOML -- so the parser, correctly,
   // never saw it and a session's enable state was silently lost.
diff --git a/src/layout_store.hpp b/src/layout_store.hpp
index c919289..eb7db18 100644
--- a/src/layout_store.hpp
+++ b/src/layout_store.hpp
@@ -8,6 +8,7 @@
 
 #include "math_channel.hpp"
 #include "measure.hpp"
+#include "source/source_config.hpp"
 
 namespace udpscope {
 
@@ -54,6 +55,12 @@ struct LayoutState {
   /// unicast; empty `interface_addr` is the default route.
   std::string multicast;
   std::string interface_addr;
+  /// Which source kind this session belongs to. Empty means `udps`: every file written before the
+  /// plugins existed. Only a kind other than `udps` is written, so a UDPS session file is
+  /// byte-identical to what earlier versions wrote.
+  std::string source_kind;
+  /// That kind's settings (`SourceConfig`), stored as top-level `source_opt_<key>` entries.
+  SourceConfig source_opts;
 
   /// The derived channels, graphs and all: the editor's work is part of the session, not of the
   /// process. A graph is stored as one string per node so the file stays in this store's TOML
@@ -144,6 +151,8 @@ struct KnownSource {
   std::uint16_t port = 0;
   std::string multicast;       ///< empty = unicast
   std::string interface_addr;  ///< empty = the default route
+  std::string kind = "udps";   ///< the session's source kind
+  SourceConfig opts;           ///< that kind's settings (empty for UDPS, whose fields are above)
   int rows = 0;                ///< plots the session had
   int signals = 0;             ///< named slots across those plots
   std::int64_t mtime = 0;      ///< orders the list; never shown
diff --git a/src/source/probe_source.cpp b/src/source/probe_source.cpp
new file mode 100644
index 0000000..218c126
--- /dev/null
+++ b/src/source/probe_source.cpp
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "source/probe_source.hpp"
+
+#include "source/registry.hpp"
+
+#include <adwaita.h>
+
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+#include <functional>
+#include <memory>
+#include <thread>
+
+namespace udpscope {
+
+ProbeSource::ProbeSource(const SourceConfig& cfg)
+    : rate_hz_(std::max(1.0, cfg.get_double("rate", 1000.0))), batch_(kBatch, 0.0) {
+  SignalInfo s;
+  s.name = "probe";
+  s.unit = "V";
+  s.type_code = 9;  // float64
+  s.rows = 1;
+  s.cols = 1;
+  s.range_min = -1.0;
+  s.range_max = 1.0;
+  s.time_mode = kTimePacket;
+  s.sampling_rate = rate_hz_;
+  signals_.push_back(s);
+}
+
+void ProbeSource::open(SourceSink& sink) {
+  sink_ = &sink;
+  configured_ = false;
+  open_.store(true, std::memory_order_relaxed);
+}
+
+void ProbeSource::close() { open_.store(false, std::memory_order_relaxed); }
+
+SourceStats ProbeSource::stats() const {
+  SourceStats s;
+  s.packets = frames_;
+  s.frames = frames_;
+  s.connected = open_.load(std::memory_order_relaxed);
+  return s;
+}
+
+void ProbeSource::poll(int timeout_ms) {
+  drain_commands();
+  if (!open_.load(std::memory_order_relaxed) || sink_ == nullptr) return;
+  if (!configured_) {
+    configured_ = true;
+    sink_->on_config(signals_, /*publish_mode=*/1);
+    sink_->on_event(SourceEvent::Connected, "");
+  }
+  // One batch takes kBatch / rate seconds to "arrive".
+  const int period_ms = std::max(1, static_cast<int>(1000.0 * kBatch / rate_hz_));
+  std::this_thread::sleep_for(std::chrono::milliseconds(std::min(period_ms, timeout_ms)));
+  const double step = 2.0 * M_PI * 5.0 / rate_hz_;  // a 5 Hz sine
+  for (std::uint32_t k = 0; k < kBatch; ++k) {
+    batch_[k] = std::sin(phase_);
+    phase_ += step;
+  }
+  values_.values = batch_.data();
+  values_.count = kBatch;
+  Frame f;
+  f.counter = counter_++;
+  f.lost = 0;
+  f.late = false;
+  f.recv_time = std::chrono::duration<double>(std::chrono::system_clock::now().time_since_epoch())
+                    .count();
+  f.publish_mode = 1;
+  f.num_samples = kBatch;
+  f.num_signals = 1;
+  f.signals = signals_.data();
+  f.values = &values_;
+  ++frames_;
+  sink_->on_data(f);
+}
+
+namespace {
+
+void on_rate_changed(GObject*, GParamSpec*, gpointer user) {
+  const auto& cb = *static_cast<std::shared_ptr<std::function<void()>>*>(user);
+  if (cb && *cb) (*cb)();
+}
+
+class ProbeKind final : public SourceKind {
+ public:
+  std::string id() const override { return "probe"; }
+  std::string display_name() const override { return "Probe (test)"; }
+  std::string identity(const SourceConfig& cfg) const override {
+    return "rate" + std::to_string(cfg.get_int("rate", 1000));
+  }
+  std::unique_ptr<DataSource> make(const SourceConfig& cfg) const override {
+    return std::make_unique<ProbeSource>(cfg);
+  }
+
+  ConfigForm make_config_form() const override {
+    GtkWidget* rate = GTK_WIDGET(adw_spin_row_new_with_range(1, 100000, 1));
+    adw_preferences_row_set_title(ADW_PREFERENCES_ROW(rate), "_Rate (Hz)");
+    adw_preferences_row_set_use_underline(ADW_PREFERENCES_ROW(rate), TRUE);
+    adw_spin_row_set_value(ADW_SPIN_ROW(rate), 1000);
+
+    auto cb = std::make_shared<std::function<void()>>();
+    g_signal_connect_data(rate, "notify::value", G_CALLBACK(on_rate_changed),
+                          new std::shared_ptr<std::function<void()>>(cb),
+                          +[](gpointer d, GClosure*) {
+                            delete static_cast<std::shared_ptr<std::function<void()>>*>(d);
+                          },
+                          static_cast<GConnectFlags>(0));
+
+    ConfigForm f;
+    f.rows = {rate};
+    f.description = "A synthetic 5 Hz sine, for the self-check";
+    f.focus = rate;
+    f.write = [=](const SourceConfig& c) {
+      adw_spin_row_set_value(ADW_SPIN_ROW(rate), static_cast<double>(c.get_int("rate", 1000)));
+    };
+    f.read = [=]() {
+      SourceConfig c;
+      c.set("rate", std::to_string(static_cast<long>(adw_spin_row_get_value(ADW_SPIN_ROW(rate)))));
+      return c;
+    };
+    f.valid = []() { return true; };
+    f.on_change = [cb](std::function<void()> fn) { *cb = std::move(fn); };
+    return f;
+  }
+};
+
+}  // namespace
+
+std::unique_ptr<SourceKind> make_probe_kind() { return std::make_unique<ProbeKind>(); }
+
+}  // namespace udpscope
diff --git a/src/source/probe_source.hpp b/src/source/probe_source.hpp
new file mode 100644
index 0000000..0e1b8ab
--- /dev/null
+++ b/src/source/probe_source.hpp
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "source/data_source.hpp"
+#include "source/source_config.hpp"
+
+#include <atomic>
+#include <cstdint>
+#include <vector>
+
+namespace udpscope {
+
+/// A synthetic source for the headless self-check: one 1 V sine signal, `kBatch` samples per
+/// frame at `rate` Hz, no socket. It exists to prove the framework end to end (open, CONFIG,
+/// data, commands, panels) and is registered only when `UDPSCOPE_PROBE_SOURCE_KINDS` is set.
+class ProbeSource final : public DataSource {
+ public:
+  static constexpr std::uint32_t kBatch = 10;
+
+  explicit ProbeSource(const SourceConfig& cfg);
+
+  void open(SourceSink& sink) override;
+  void poll(int timeout_ms) override;
+  void close() override;
+  SourceStats stats() const override;
+  bool connected() const override { return open_.load(std::memory_order_relaxed); }
+
+  /// What a panel command does, so the probe can see that `post()` reached the producer thread.
+  void note_applied() noexcept { applied_.fetch_add(1, std::memory_order_relaxed); }
+  std::uint64_t commands_applied() const noexcept {
+    return applied_.load(std::memory_order_relaxed);
+  }
+
+ private:
+  double rate_hz_;
+  SourceSink* sink_ = nullptr;
+  std::atomic<bool> open_{false};
+  bool configured_ = false;
+  std::uint32_t counter_ = 0;
+  std::uint64_t frames_ = 0;
+  double phase_ = 0.0;
+  std::vector<SignalInfo> signals_;
+  std::vector<double> batch_;
+  SignalValues values_;
+  std::atomic<std::uint64_t> applied_{0};
+};
+
+}  // namespace udpscope
diff --git a/src/source/registry.cpp b/src/source/registry.cpp
index 2c2f1ac..5b06128 100644
--- a/src/source/registry.cpp
+++ b/src/source/registry.cpp
@@ -50,7 +50,7 @@ void register_builtin_sources() {
   if (done) return;
   done = true;
   register_kind(make_udps_kind());
-  // Task 6: register make_probe_kind() when UDPSCOPE_PROBE_SOURCE_KINDS is set
+  if (std::getenv("UDPSCOPE_PROBE_SOURCE_KINDS") != nullptr) register_kind(make_probe_kind());
 }
 
 std::string session_host(const std::string& kind_id, const SourceConfig& cfg) {
diff --git a/src/ui.cpp b/src/ui.cpp
index 959554e..60a8cb6 100644
--- a/src/ui.cpp
+++ b/src/ui.cpp
@@ -33,6 +33,7 @@
 #include "model.hpp"
 #include "plot_host.hpp"
 #include "search.hpp"
+#include "source/registry.hpp"
 #include "source_dialog.hpp"
 
 #include <adwaita.h>
@@ -100,8 +101,7 @@ void open_configurations(App& app) {
 
   GtkWidget* title = gtk_label_new(nullptr);
   gtk_label_set_markup(GTK_LABEL(title),
-                       ("<b>" + app.source_host + ":" + std::to_string(app.source_port) +
-                        "</b>")
+                       ("<b>" + app.source_title + "</b>")
                            .c_str());
   gtk_widget_set_halign(title, GTK_ALIGN_START);
   gtk_box_append(GTK_BOX(box), title);
@@ -5918,6 +5918,14 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
   app.source_port = cfg.open_waveform.empty() ? cfg.session_port() : 0;
   app.source_multicast = cfg.open_waveform.empty() ? cfg.multicast : std::string();
   app.source_interface = cfg.interface_addr;
+  app.source_kind = cfg.source_kind;
+  app.source_opts = cfg.source_opts;
+  if (cfg.source_kind != "udps" && find_kind(cfg.source_kind) != nullptr) {
+    app.source_title = find_kind(cfg.source_kind)->display_name() + " " +
+                       find_kind(cfg.source_kind)->identity(cfg.source_config());
+  } else {
+    app.source_title = app.source_host + ":" + std::to_string(app.source_port);
+  }
   // The event cache is keyed on the source, like the packet capture. A waveform has no source, so a
   // file-mode run has no cache either -- there are no latches in a file.
   if (!app.source_host.empty() && app.source_port != 0) {
diff --git a/src/ui_app.hpp b/src/ui_app.hpp
index 2af2da5..144e5a6 100644
--- a/src/ui_app.hpp
+++ b/src/ui_app.hpp
@@ -29,6 +29,7 @@
 #include "plot_host.hpp"
 #include "search.hpp"
 #include "settings.hpp"
+#include "source/source_config.hpp"
 #include "ui_prefs.hpp"
 #include "shortcuts.hpp"
 #include "status_text.hpp"
@@ -837,6 +838,11 @@ struct App {
   /// chooser needs both to reconnect to a multicast source from a stored row.
   std::string source_multicast;
   std::string source_interface;
+  /// The source kind and its settings, so the session can say which kind it belongs to, and the
+  /// words that name the source in dialogs (`host:port` for UDPS, `<kind> <identity>` otherwise).
+  std::string source_kind = "udps";
+  SourceConfig source_opts;
+  std::string source_title;
   guint layout_save_source = 0;
   bool layout_loaded = false;
   unsigned signal_generation = ~0u;
diff --git a/src/ui_layout.cpp b/src/ui_layout.cpp
index d6c059f..329dc57 100644
--- a/src/ui_layout.cpp
+++ b/src/ui_layout.cpp
@@ -97,6 +97,8 @@ LayoutState collect_layout(App& app) {
   // The connection is the session's too: the file's name carries only host and port.
   st.multicast = app.source_multicast;
   st.interface_addr = app.source_interface;
+  st.source_kind = app.source_kind;
+  st.source_opts = app.source_opts;
   // The configuration's own identity and the startup settings it carries. The buffer size is a
   // *startup* parameter -- the rings are allocated before any stream is known -- so a configuration
   // is the only place it can be remembered per source, and the chooser applies it on open.