diff --git a/.gitignore b/.gitignore
index 83138ed..abeb59a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,6 +18,7 @@ test/test_json_glib
 test/test_strlen
 test/test_text
 test/test_table
+test/test_packet_id
 test/var_is_routing
 test/var_type
 test/uniform_parse
diff --git a/include/psyc.h b/include/psyc.h
index 9a1a7bb..41ace37 100644
--- a/include/psyc.h
+++ b/include/psyc.h
@@ -164,6 +164,13 @@ psyc_dict_lookup_int (const PsycDictInt * dict, size_t size,
 				       inherit, tmp);
 }
 
+#include "psyc/syntax.h"
+#include "psyc/method.h"
+#include "psyc/packet.h"
+#include "psyc/parse.h"
+#include "psyc/render.h"
+#include "psyc/text.h"
+#include "psyc/uniform.h"
 #include "psyc/variable.h"
 
 #endif
diff --git a/include/psyc/method.h b/include/psyc/method.h
index cb41300..9bbac06 100644
--- a/include/psyc/method.h
+++ b/include/psyc/method.h
@@ -26,6 +26,7 @@ typedef enum PsycMethod {
     PSYC_MC_NOTICE,
     PSYC_MC_NOTICE_CONTEXT_ENTER,
     PSYC_MC_NOTICE_CONTEXT_LEAVE,
+    PSYC_MC_NOTICE_HELLO,
     PSYC_MC_REQUEST,
     PSYC_MC_REQUEST_CONTEXT_ENTER,
     PSYC_MC_REQUEST_CONTEXT_LEAVE,
diff --git a/include/psyc/packet.h b/include/psyc/packet.h
index 7eecd0c..4f37750 100644
--- a/include/psyc/packet.h
+++ b/include/psyc/packet.h
@@ -68,6 +68,15 @@ typedef enum {
     PSYC_STATE_RESYNC = '?',
 } PsycStateOp;
 
+typedef enum {
+    PSYC_PACKET_ID_CONTEXT = 0,
+    PSYC_PACKET_ID_SOURCE = 1,
+    PSYC_PACKET_ID_TARGET = 2,
+    PSYC_PACKET_ID_COUNTER = 3,
+    PSYC_PACKET_ID_FRAGMENT = 4,
+    PSYC_PACKET_ID_ELEMS = 5,
+} PsycPacketId;
+
 /** Structure for a modifier. */
 typedef struct {
     char oper;
@@ -209,6 +218,11 @@ psyc_packet_init_raw (PsycPacket *packet,
 		      char *content, size_t contentlen,
 		      PsycPacketFlag flag);
 
+/** Get the total length of a packet ID when rendered. */
+size_t
+psyc_packet_id_length (size_t contextlen, size_t sourcelen, size_t targetelen,
+		       size_t counterlen, size_t fragmentlen);
+
 /** @} */ // end of packet group
 
 #endif
diff --git a/include/psyc/render.h b/include/psyc/render.h
index 4a826db..7563ece 100644
--- a/include/psyc/render.h
+++ b/include/psyc/render.h
@@ -63,6 +63,14 @@ psyc_render_list (PsycList *list, char *buffer, size_t buflen);
 PsycRenderRC
 psyc_render_table (PsycTable *table, char *buffer, size_t buflen);
 
+PsycRenderRC
+psyc_render_packet_id (char *context, size_t contextlen,
+		       char *source, size_t sourcelen,
+		       char *target, size_t targetlen,
+		       char *counter, size_t counterlen,
+		       char *fragment, size_t fragmentlen,
+		       char *buffer, size_t buflen);
+
 /** @} */ // end of render group
 
 #endif
diff --git a/src/packet.c b/src/packet.c
index c61ee8d..17bd207 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -197,3 +197,10 @@ psyc_packet_init_raw (PsycPacket *p,
 
     psyc_packet_length_set(p);
 }
+
+size_t
+psyc_packet_id_length (size_t contextlen, size_t sourcelen, size_t targetlen,
+		       size_t counterlen, size_t fragmentlen)
+{
+    return contextlen + sourcelen + targetlen + counterlen + fragmentlen + 5;
+}
diff --git a/src/render.c b/src/render.c
index 0db289d..f0a93fe 100644
--- a/src/render.c
+++ b/src/render.c
@@ -146,3 +146,29 @@ psyc_render (PsycPacket * packet, char *buffer, size_t buflen)
     assert(cur == packet->length);
     return PSYC_RENDER_SUCCESS;
 }
+
+PsycRenderRC
+psyc_render_packet_id (char *context, size_t contextlen,
+		       char *source, size_t sourcelen,
+		       char *target, size_t targetlen,
+		       char *counter, size_t counterlen,
+		       char *fragment, size_t fragmentlen,
+		       char *buffer, size_t buflen)
+{
+    PsycList list;
+    PsycString elems[PSYC_PACKET_ID_ELEMS] = {};
+
+    if (contextlen)
+	elems[PSYC_PACKET_ID_CONTEXT] = PSYC_STRING(context, contextlen);
+    if (sourcelen)
+	elems[PSYC_PACKET_ID_SOURCE] = PSYC_STRING(source, sourcelen);
+    if (targetlen)
+	elems[PSYC_PACKET_ID_TARGET] = PSYC_STRING(target, targetlen);
+    if (counterlen)
+	elems[PSYC_PACKET_ID_COUNTER] = PSYC_STRING(counter, counterlen);
+    if (fragmentlen)
+	elems[PSYC_PACKET_ID_FRAGMENT] = PSYC_STRING(fragment, fragmentlen);
+
+    psyc_list_init(&list, elems, PSYC_PACKET_ID_ELEMS, PSYC_LIST_NO_LENGTH);
+    return psyc_render_list(&list, buffer, buflen);
+}
diff --git a/test/Makefile b/test/Makefile
index ba570c3..123de1b 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -3,7 +3,7 @@ DEBUG = 2
 CFLAGS = -I../include -I../src -Wall -std=c99 ${OPT}
 LDFLAGS = -L../lib
 LOADLIBES = -lpsyc -lm
-TARGETS = test_psyc test_psyc_speed test_parser test_match test_render test_text var_is_routing var_type uniform_parse test_table
+TARGETS = test_psyc test_psyc_speed test_parser test_match test_render test_text var_is_routing var_type uniform_parse test_list test_table test_packet_id
 O = test.o
 WRAPPER =
 DIET = diet
@@ -48,7 +48,9 @@ test: ${TARGETS}
 	./var_is_routing
 	./var_type
 	./uniform_parse
+	./test_list
 	./test_table
+	./test_packet_id
 	x=0; for f in packets/[0-9]*; do echo ">> $$f"; ./test_psyc -f $$f | ${DIFF} -u $$f -; x=$$((x+$$?)); done; exit $$x
 	x=0; for f in packets/[0-9]*; do echo ">> $$f"; ./test_psyc -rf $$f | ${DIFF} -u $$f -; x=$$((x+$$?)); done; exit $$x
 
diff --git a/test/test_packet_id.c b/test/test_packet_id.c
new file mode 100644
index 0000000..c42de6e
--- /dev/null
+++ b/test/test_packet_id.c
@@ -0,0 +1,70 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+#include <psyc.h>
+#include <psyc/packet.h>
+#include <psyc/render.h>
+
+int
+packet_id (char *context, size_t contextlen,
+	   char *source, size_t sourcelen,
+	   char *target, size_t targetlen,
+	   char *counter, size_t counterlen,
+	   char *fragment, size_t fragmentlen,
+	   char *result, size_t resultlen)
+{
+    size_t idlen = psyc_packet_id_length(contextlen, sourcelen, targetlen,
+					 counterlen, fragmentlen);
+    char *id = malloc(idlen);
+    psyc_render_packet_id(context, contextlen,
+			  source, sourcelen,
+			  target, targetlen,
+			  counter, counterlen,
+			  fragment, fragmentlen,
+			  id, idlen);
+    printf("%.*s\n", (int)idlen, id);
+    int ret = idlen == resultlen && memcmp(result, id, idlen) == 0;
+    free(id);
+    return ret;
+}
+
+int
+main (int argc, char **argv)
+{
+    if (!packet_id(PSYC_C2ARG(""),
+		   PSYC_C2ARG("psyc://example.net/~alice"),
+		   PSYC_C2ARG("psyc://example.net/~bob"),
+		   PSYC_C2ARG("1337"),
+		   PSYC_C2ARG("42"),
+		   PSYC_C2ARG("||psyc://example.net/~alice|psyc://example.net/~bob"
+			      "|1337|42")))
+	return 1;
+
+    if (!packet_id(PSYC_C2ARG("psyc://example.net/@bar"),
+		   PSYC_C2ARG("psyc://example.net/~alice"),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG("1337"),
+		   PSYC_C2ARG("42"),
+		   PSYC_C2ARG("|psyc://example.net/@bar|psyc://example.net/~alice|"
+			      "|1337|42")))
+	return 2;
+
+    if (!packet_id(PSYC_C2ARG("psyc://example.net/@bar"),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG("psyc://example.net/~alice"),
+		   PSYC_C2ARG("1337"),
+		   PSYC_C2ARG("42"),
+		   PSYC_C2ARG("|psyc://example.net/@bar||psyc://example.net/~alice"
+			      "|1337|42")))
+	return 3;
+
+    if (!packet_id(PSYC_C2ARG("psyc://example.net/@bar"),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG(""),
+		   PSYC_C2ARG("|psyc://example.net/@bar||||")))
+	return 4;
+
+    return 0;
+}