diff --git a/contrib/opentracing/include/vars.h b/contrib/opentracing/include/vars.h
new file mode 100644
index 0000000..5ce8879
--- /dev/null
+++ b/contrib/opentracing/include/vars.h
@@ -0,0 +1,49 @@
+/***
+ * Copyright 2020 HAProxy Technologies
+ *
+ * This file is part of the HAProxy OpenTracing filter.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#ifndef _OPENTRACING_VARS_H_
+#define _OPENTRACING_VARS_H_
+
+#define FLT_OT_VARS_SCOPE       "txn"
+#define FLT_OT_VAR_CHAR_DASH    'D'
+#define FLT_OT_VAR_CHAR_SPACE   'S'
+
+
+#ifndef DEBUG_OT
+#  define flt_ot_vars_dump(...)   while (0)
+#else
+void                 flt_ot_vars_dump(struct stream *s);
+#endif
+int                  flt_ot_var_register(const char *scope, const char *prefix, const char *name, char **err);
+int                  flt_ot_var_set(struct stream *s, const char *scope, const char *prefix, const char *name, const char *value, uint opt, char **err);
+int                  flt_ot_var_unset(struct stream *s, const char *scope, const char *prefix, const char *name, uint opt, char **err);
+int                  flt_ot_vars_unset(struct stream *s, const char *scope, const char *prefix, uint opt, char **err);
+int                  flt_ot_var_get(struct stream *s, const char *scope, const char *prefix, const char *name, char **value, uint opt, char **err);
+struct otc_text_map *flt_ot_vars_get(struct stream *s, const char *scope, const char *prefix, uint opt, char **err);
+
+#endif /* _OPENTRACING_VARS_H_ */
+
+/*
+ * Local variables:
+ *  c-indent-level: 8
+ *  c-basic-offset: 8
+ * End:
+ *
+ * vi: noexpandtab shiftwidth=8 tabstop=8
+ */