diff --git a/include/memory.h b/include/memory.h
index 3d137e3..6953970 100644
--- a/include/memory.h
+++ b/include/memory.h
@@ -74,7 +74,7 @@ typedef struct st_r3_buffer_prototype_t r3_buffer_prototype_t;
  * buffer structure compatible with iovec
  */
 typedef struct st_r3_iovec_t {
-    char *base;
+    const char *base;
     unsigned int len;
 } r3_iovec_t;
 
diff --git a/include/r3_slug.h b/include/r3_slug.h
index 76936ae..78da8c4 100644
--- a/include/r3_slug.h
+++ b/include/r3_slug.h
@@ -13,11 +13,11 @@ extern "C" {
 
 char * r3_slug_compile(const char * str, unsigned int len);
 
-char * r3_slug_find_pattern(const char *s1, unsigned int str_len, unsigned int *len);
+const char * r3_slug_find_pattern(const char *s1, unsigned int str_len, unsigned int *len);
 
-char * r3_slug_find_name(const char *s1, unsigned int str_len, unsigned int *len);
+const char * r3_slug_find_name(const char *s1, unsigned int str_len, unsigned int *len);
 
-char * r3_slug_find_placeholder(const char *s1, unsigned int str_len, unsigned int *len);
+const char * r3_slug_find_placeholder(const char *s1, unsigned int str_len, unsigned int *len);
 
 int r3_slug_count(const char * needle, int len, char **errstr);
 
diff --git a/include/str_array.h b/include/str_array.h
index 0663317..778c807 100644
--- a/include/str_array.h
+++ b/include/str_array.h
@@ -26,7 +26,7 @@ bool str_array_slugs_full(const str_array * l);
 
 // bool str_array_append_slug(str_array * l, char * slug);
 
-bool str_array_append(str_array * l, char * token, unsigned int len);
+bool str_array_append(str_array * l, const char * token, unsigned int len);
 
 void str_array_free(str_array *l);
 
diff --git a/src/edge.c b/src/edge.c
index 666c595..b0562b4 100644
--- a/src/edge.c
+++ b/src/edge.c
@@ -64,7 +64,7 @@ R3Node * r3_edge_branch(R3Edge *e, int dl) {
     R3Edge * new_edge;
 
     // the rest string
-    char * s1 = e->pattern.base + dl;
+    const char * s1 = e->pattern.base + dl;
     int s1_len = e->pattern.len - dl;
 
     // the suffix edge of the leaf
diff --git a/src/node.c b/src/node.c
index 8088a6d..cfa25e5 100644
--- a/src/node.c
+++ b/src/node.c
@@ -28,8 +28,8 @@
 // String value as the index http://judy.sourceforge.net/doc/JudySL_3x.htm
 
 
-static int strndiff(char * d1, char * d2, unsigned int n) {
-    char * o = d1;
+static int strndiff(const char * d1, const char * d2, unsigned int n) {
+    const char * o = d1;
     while ( *d1 == *d2 && n-- > 0 ) {
         d1++;
         d2++;
@@ -505,7 +505,7 @@ void r3_route_free(R3Route * route) {
 //     return route->slugs != NULL;
 // }
 
-static r3_iovec_t* router_append_slug(R3Route * route, char * slug, unsigned int len) {
+static r3_iovec_t* router_append_slug(R3Route * route, const char * slug, unsigned int len) {
     r3_iovec_t *temp;
     r3_vector_reserve(NULL, &route->slugs, route->slugs.size + 1);
     temp = route->slugs.entries + route->slugs.size++;
@@ -515,10 +515,10 @@ static r3_iovec_t* router_append_slug(R3Route * route, char * slug, unsigned int
 }
 
 static void get_slugs(R3Route * route, const char * path, int path_len) {
-    char *plh = (char*)path;
+    const char *plh = path;
     unsigned int l, namel;
     l = 0;
-    char *name;
+    const char *name;
     while (plh < (path + path_len)) {
         plh = r3_slug_find_placeholder(plh+l, path_len, &l);
         if (!plh) break;
@@ -681,7 +681,7 @@ R3Node * r3_tree_insert_pathl_ex(R3Node *tree, const char *path, unsigned int pa
         info("slug_cnt: %d\n",slug_cnt);
         if ( slug_cnt > 1 ) {
             unsigned int   slug_len;
-            char *p = r3_slug_find_placeholder(path, path_len, &slug_len);
+            const char *p = r3_slug_find_placeholder(path, path_len, &slug_len);
 
 #ifdef DEBUG
             assert(p);
@@ -707,9 +707,9 @@ R3Node * r3_tree_insert_pathl_ex(R3Node *tree, const char *path, unsigned int pa
             if (slug_cnt == 1) {
                 // there is one slug, let's see if it's optimiz-able by opcode
                 unsigned int   slug_len = 0;
-                char *slug_p = r3_slug_find_placeholder(path, path_len, &slug_len);
+                const char *slug_p = r3_slug_find_placeholder(path, path_len, &slug_len);
                 unsigned int   slug_pattern_len = 0;
-                char *slug_pattern = r3_slug_find_pattern(slug_p, slug_len, &slug_pattern_len);
+                const char *slug_pattern = r3_slug_find_pattern(slug_p, slug_len, &slug_pattern_len);
 
                 int opcode = 0;
                 // if there is a pattern defined.
diff --git a/src/str.c b/src/str.c
index aca5015..26e180b 100644
--- a/src/str.c
+++ b/src/str.c
@@ -15,7 +15,7 @@
 #include "slug.h"
 #include "zmalloc.h"
 
-static char * strnchr(const char* str, unsigned int len, int ch) {
+static const char * strnchr(const char* str, unsigned int len, int ch) {
     for (unsigned int i = 0; i < len; i++) {
         if (str[i] == ch) return str + i;
     }
@@ -86,9 +86,9 @@ char * r3_inside_slug(const char * needle, int needle_len, char *offset, char **
     return NULL;
 }
 
-char * r3_slug_find_placeholder(const char *s1, unsigned int str_len, unsigned int *len) {
-    char *c;
-    char *s2;
+const char * r3_slug_find_placeholder(const char *s1, unsigned int str_len, unsigned int *len) {
+    const char *c;
+    const char *s2;
     int cnt = 0;
     if (c = strnchr(s1, str_len, '{')) {
         // find closing '}'
@@ -119,9 +119,9 @@ char * r3_slug_find_placeholder(const char *s1, unsigned int str_len, unsigned i
 /**
  * given a slug string, duplicate the pattern string of the slug
  */
-char * r3_slug_find_pattern(const char *s1, unsigned int str_len, unsigned int *len) {
-    char *c;
-    char *s2;
+const char * r3_slug_find_pattern(const char *s1, unsigned int str_len, unsigned int *len) {
+    const char *c;
+    const char *s2;
     unsigned int cnt = 1;
     if ( (c = strnchr(s1, str_len, ':')) ) {
         c++;
@@ -152,9 +152,9 @@ char * r3_slug_find_pattern(const char *s1, unsigned int str_len, unsigned int *
 /**
  * given a slug string, duplicate the parameter name string of the slug
  */
-char * r3_slug_find_name(const char *s1, unsigned int str_len, unsigned int *len) {
-    char * c;
-    char * s2;
+const char * r3_slug_find_name(const char *s1, unsigned int str_len, unsigned int *len) {
+    const char * c;
+    const char * s2;
     int cnt = 0;
     unsigned int plholder;
     if (c = r3_slug_find_placeholder(s1, str_len, &plholder)) {
@@ -177,8 +177,9 @@ char * r3_slug_find_name(const char *s1, unsigned int str_len, unsigned int *len
  */
 char * r3_slug_compile(const char * str, unsigned int len)
 {
-    char *s1 = NULL, *o = NULL;
-    char *pat = NULL;
+    const char *s1 = NULL;
+    char *o = NULL;
+    const char *pat = NULL;
     char sep = '/';
 
 
diff --git a/src/token.c b/src/token.c
index 6464beb..77f8cb2 100644
--- a/src/token.c
+++ b/src/token.c
@@ -20,7 +20,7 @@ void str_array_free(str_array *l) {
     free(l->tokens.entries);
 }
 
-bool str_array_append(str_array * l, char * token, unsigned int len) {
+bool str_array_append(str_array * l, const char * token, unsigned int len) {
     R3_VECTOR(r3_iovec_t) *tks = &l->tokens;
     r3_vector_reserve(NULL, tks, tks->size + 1);
     r3_iovec_t *temp = tks->entries + tks->size++;