diff --git a/libthapictl/thapi-ctl.h b/libthapictl/thapi-ctl.h
index bee54d9f..0bfaca32 100644
--- a/libthapictl/thapi-ctl.h
+++ b/libthapictl/thapi-ctl.h
@@ -4,7 +4,29 @@
 extern "C" {
 #endif
 
+/**
+ * Start tracing host and device events, when application is run with iprof.
+ *
+ * Does nothing if not run with iprof. This is detected using the
+ * THAPI_LTTNG_SESSION_ID environment variable.
+ *
+ * @return 0 on success
+ */
 int thapi_start_tracing();
+
+/**
+ * Stop tracing host and device events, when application is run with iprof.
+ *
+ * NOTE: must not be called until after any device runtime initialization is
+ * complete, in case dynamic symbols are loaded. For CUDA, calling `cudaFree(0)`
+ * will force all symbols be loaded and not doing anything else, and make it
+ * safe to call thapi_stop_tracing.
+ *
+ * Does nothing if not run with iprof. This is detected using the
+ * THAPI_LTTNG_SESSION_ID environment variable.
+ *
+ * @return 0 on success
+ */
 int thapi_stop_tracing();
  
 #ifdef __cplusplus