diff --git a/Makefile b/Makefile
index d3a45c9..d0e09d2 100644
--- a/Makefile
+++ b/Makefile
@@ -15,13 +15,14 @@ dep:
 	$(CC) -I/usr/local/include -MM *.c > makefile.depend
 
 activitypub.o: activitypub.c xs.h xs_encdec.h xs_json.h xs_curl.h \
- xs_mime.h xs_openssl.h snac.h
+ xs_mime.h xs_openssl.h xs_regex.h snac.h
 data.o: data.c xs.h xs_io.h xs_json.h xs_openssl.h snac.h
-html.o: html.c xs.h xs_io.h xs_json.h xs_regex.h snac.h
+html.o: html.c xs.h xs_io.h xs_encdec.h xs_json.h xs_regex.h xs_set.h \
+ snac.h
 http.o: http.c xs.h xs_io.h xs_encdec.h xs_openssl.h xs_curl.h snac.h
 httpd.o: httpd.c xs.h xs_io.h xs_encdec.h xs_json.h xs_socket.h \
  xs_httpd.h snac.h
 main.o: main.c xs.h xs_io.h xs_encdec.h xs_json.h snac.h
 snac.o: snac.c xs.h xs_io.h xs_encdec.h xs_json.h xs_curl.h xs_openssl.h \
- xs_socket.h xs_httpd.h xs_mime.h xs_regex.h snac.h
+ xs_socket.h xs_httpd.h xs_mime.h xs_regex.h xs_set.h snac.h
 webfinger.o: webfinger.c xs.h xs_encdec.h xs_json.h xs_curl.h snac.h
diff --git a/html.c b/html.c
index 21ee151..1e7788d 100644
--- a/html.c
+++ b/html.c
@@ -6,6 +6,7 @@
 #include "xs_encdec.h"
 #include "xs_json.h"
 #include "xs_regex.h"
+#include "xs_set.h"
 
 #include "snac.h"
 
diff --git a/snac.c b/snac.c
index d0ab4e9..3c9fd40 100644
--- a/snac.c
+++ b/snac.c
@@ -13,6 +13,7 @@
 #include "xs_httpd.h"
 #include "xs_mime.h"
 #include "xs_regex.h"
+#include "xs_set.h"
 
 #include "snac.h"
 
diff --git a/xs_set.h b/xs_set.h
new file mode 100644
index 0000000..c983ce6
--- /dev/null
+++ b/xs_set.h
@@ -0,0 +1,95 @@
+/* copyright (c) 2022 grunfink - MIT license */
+
+#ifndef _XS_SET_H
+
+#define _XS_SET_H
+
+typedef struct _xs_set {
+    int elems;              /* number of hash entries */
+    int used;               /* number of used hash entries */
+    d_char *list;           /* list of stored data */
+    int hash[0];            /* hashed offsets */
+} xs_set;
+
+xs_set *xs_set_new(int elems);
+void xs_set_free(xs_set *s);
+int xs_set_add(xs_set *s, char *data);
+
+
+#ifdef XS_IMPLEMENTATION
+
+xs_set *xs_set_new(int elems)
+/* creates a new set with a maximum of size hashed data */
+{
+    int sz = sizeof(struct _xs_set) + sizeof(int) * elems;
+    xs_set *s = calloc(sz, 1);
+
+    /* initialize */
+    s->elems  = elems;
+    s->list   = xs_list_new();
+
+    return s;
+}
+
+
+void xs_set_free(xs_set *s)
+/* frees a set */
+{
+    free(s->list);
+    free(s);
+}
+
+
+unsigned int _xs_set_hash(char *data, int size)
+{
+    unsigned int hash = 0x666;
+    int n;
+
+    for (n = 0; n < size; n++) {
+        hash ^= data[n];
+        hash *= 111111111;
+    }
+
+    return hash ^ hash >> 16;
+}
+
+
+int xs_set_add(xs_set *s, char *data)
+/* adds the data to the set */
+/* returns: 1 if added, 0 if already there, -1 if it's full */
+{
+    unsigned int hash, i;
+    int sz = xs_size(data);
+
+    hash = _xs_set_hash(data, sz);
+
+    while (s->hash[(i = hash % s->elems)]) {
+        /* get the pointer to the stored data */
+        char *p = &s->list[s->hash[i]];
+
+        /* already here? */
+        if (memcmp(p, data, sz) == 0)
+            return 0;
+
+        /* try next value */
+        hash++;
+    }
+
+    /* is it full? fail */
+    if (s->used == s->elems / 2)
+        return -1;
+
+    /* store the position */
+    s->hash[i] = xs_size(s->list);
+
+    /* add the data */
+    s->list = xs_list_append_m(s->list, data, sz);
+
+    s->used++;
+
+    return 1;
+}
+
+#endif /* XS_IMPLEMENTATION */
+
+#endif /* XS_SET_H */
\ No newline at end of file