diff --git a/strings.c b/strings.c
index 2dd7bed..79e6df4 100644
--- a/strings.c
+++ b/strings.c
@@ -50,7 +50,7 @@ size_t str_strlcpy(char *dst, const char *src, size_t len)
     register size_t n = len;
 
     assert(src);
-    assert(dst);
+    assert(dst || len==0);
     /* Copy as many bytes as will fit */
     if (n != 0 && --n != 0) {
         do {
@@ -430,6 +430,101 @@ const char *str_escape_ex(const char *str, char *buffer, size_t size, const char
     return buffer;
 }
 
+size_t str_format(char *dst, size_t size, const char *format, const char *params[], size_t nparams)
+{
+    const char *pos, *copy = format;
+    char *write = dst;
+
+    size_t space = size;
+    size_t space_needed = 0;
+
+    for (pos = format; *pos; ++pos) {
+        pos = strpbrk(pos, "{\\");
+        if (!pos) {
+            /* no more tokens, copy remainder of format string to output */
+            space_needed += str_strlcpy(write, copy, space);
+            break;
+        }
+        else {
+            size_t bytes = pos - copy;
+            /* found the start of a new token, copy `bytes` of lead text from [copy, pos) */
+            space_needed += bytes;
+            if (space > 0) {
+                if (bytes >= space) {
+                    bytes = space - 1;
+                }
+                str_strlcpy(write, copy, bytes + 1);
+                write += bytes;
+                space -= bytes;
+            }
+        }
+        if (*pos == '{') {
+            const char *token = pos + 1;
+
+            copy = strchr(pos, '}');
+            if (!copy) {
+                /* syntax error: unterminated token */
+                return 0;
+            }
+            else {
+                /* found a token in the [token, copy) interval */
+                size_t keylen = copy - token;
+                size_t n;
+                const char *val = NULL;
+                for (n = 0; n != nparams; ++n) {
+                    const char *key = params[n];
+                    if (0 == strncmp(key, token, keylen)) {
+                        /* param matches token? */
+                        if (key[keylen] == '\0') {
+                            val = key + keylen + 1;
+                            break;
+                        }
+                    }
+                }
+                if (val) {
+                    size_t slen = str_strlcpy(write, val, space);
+                    space_needed += slen;
+                    if (slen < space) {
+                        space -= slen;
+                        write += slen;
+                    }
+                    else {
+                        /* buffer is full */
+                        write += space - 1;
+                        space = 0;
+                    }
+                }
+                else {
+                    /* token not found, copy [pos, copy] to output instead */
+                    size_t bytes = keylen + 2;
+                    space_needed += bytes;
+                    if (bytes >= space) {
+                        bytes = space - 1;
+                    }
+                    str_strlcpy(write, pos, bytes + 1);
+                    write += bytes;
+                    space -= bytes;
+                }
+                pos = ++copy;
+            }
+        }
+        else {
+            /** backslash escapes the next character */
+            ++space_needed;
+            if (pos[1]) ++pos;
+            if (space > 1) {
+                *write++ = *pos;
+                --space;
+            }
+            copy = pos + 1;
+        }
+    }
+    if (copy < pos) {
+        space_needed += str_strlcpy(write, copy, space);
+    }
+    return space_needed;
+}
+
 const char *str_escape(const char *str, char *buffer, size_t size) {
     return str_escape_ex(str, buffer, size, "\n\t\r\'\"\\");
 }
diff --git a/strings.h b/strings.h
index d0f94cb..1daf684 100644
--- a/strings.h
+++ b/strings.h
@@ -10,6 +10,7 @@ size_t str_strlcpy(char *dst, const char *src, size_t len);
 size_t str_strlcat(char *dst, const char *src, size_t len);
 char *str_strdup(const char *s);
 
+size_t str_format(char *dst, size_t size, const char *format, const char *params[], size_t nparams);
 const char *str_escape(const char *str, char *buffer, size_t size);
 const char *str_escape_ex(const char *str, char *buffer, size_t size, const char *chars);
 char *str_unescape(char *str);
diff --git a/test_strings.c b/test_strings.c
index 05b13c5..2445dcb 100644
--- a/test_strings.c
+++ b/test_strings.c
@@ -117,6 +117,7 @@ static void test_str_strlcpy(CuTest * tc)
 
     memset(buffer, 0x7f, sizeof(buffer));
 
+    CuAssertIntEquals(tc, 8, (int)str_strlcpy(NULL, "herpderp", 0));
     CuAssertIntEquals(tc, 4, (int)str_strlcpy(buffer, "herp", 8));
     CuAssertStrEquals(tc, "herp", buffer);
     CuAssertIntEquals(tc, 0x7f, buffer[5]);
@@ -143,6 +144,85 @@ static void test_str_itoa(CuTest * tc)
     CuAssertStrEquals(tc, "-1234567890", str_itoa(-1234567890));
 }
 
+static void test_str_format(CuTest *tc)
+{
+    const char *params[] = {
+        "name\0Enno",
+        "time\0now"
+    };
+    char buffer[64];
+    /* no tokens */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 11, (int)str_format(NULL, 0, "Hello World", NULL, 0));
+    CuAssertIntEquals(tc, 11, (int) str_format(buffer, 64, "Hello World", NULL, 0));
+    CuAssertStrEquals(tc, "Hello World", buffer);
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 11, (int)str_format(buffer, 12, "Hello World", NULL, 0));
+    CuAssertStrEquals(tc, "Hello World", buffer);
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 11, (int)str_format(buffer, 11, "Hello World", NULL, 0));
+    CuAssertStrEquals(tc, "Hello Worl", buffer);
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 11, (int)str_format(buffer, 64, "Hello World", params, 2));
+    CuAssertStrEquals(tc, "Hello World", buffer);
+
+    /* unterminated token error */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 0, (int)str_format(buffer, 64, "Hello {world", NULL, 0));
+
+    /* token not found */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 13, (int)str_format(buffer, 64, "Hello {world}", NULL, 0));
+    CuAssertStrEquals(tc, "Hello {world}", buffer);
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 13, (int)str_format(buffer, 64, "Hello {world}", params, 2));
+    CuAssertStrEquals(tc, "Hello {world}", buffer);
+
+    /* happy case, find a token and replace it */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 10, (int)str_format(buffer, 64, "Hello {name}", params, 2));
+    CuAssertStrEquals(tc, "Hello Enno", buffer);
+
+    /* repeat tokens */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 12, (int)str_format(buffer, 64, "{name} is {name}", params, 2));
+    CuAssertStrEquals(tc, "Enno is Enno", buffer);
+
+    /* multiple tokens */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 28, (int)str_format(buffer, 29, "Hello {name}, the time is {time}.", params, 2));
+    CuAssertStrEquals(tc, "Hello Enno, the time is now.", buffer);
+
+    /* escaping braces */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 12, (int)str_format(buffer, 64, "Hello \\{name\\}", params, 2));
+    CuAssertStrEquals(tc, "Hello {name}", buffer);
+
+    /* escape other characters */
+    memset(buffer, 0, sizeof(buffer));
+    CuAssertIntEquals(tc, 13, (int)str_format(buffer, 64, "Hello \\\\\\World\\", params, 2));
+    CuAssertStrEquals(tc, "Hello \\World\\", buffer);
+
+
+#if 0
+
+    /* buffer too short */
+    CuAssertStrEquals(tc, "Hello", str_format(buffer, 6, "Hello {name}", params, 2));
+
+    /* escaped braces */
+    CuAssertStrEquals(tc, "Hello {name}!", str_format(buffer, 64, "Hello \\{name\\}!", params, 2));
+
+    /* escaped backslashes */
+    CuAssertStrEquals(tc, "Hello \\Enno!", str_format(buffer, 64, "Hello \\\\{name}!", params, 2));
+
+    /* ignore garbage single backslash */
+    CuAssertStrEquals(tc, "", str_format(buffer, 64, "\\", params, 2));
+
+    /* syntax error (missing }) */
+    CuAssertPtrEquals(tc, NULL, str_format(buffer, 64, "Hello {name", params, 2));
+#endif
+}
+
 static void test_sbstring(CuTest * tc)
 {
     char buffer[16];
@@ -293,6 +373,7 @@ void add_suite_strings(CuSuite *suite)
     SUITE_ADD_TEST(suite, test_str_strlcat);
     SUITE_ADD_TEST(suite, test_str_strlcpy);
     SUITE_ADD_TEST(suite, test_str_itoa);
+    SUITE_ADD_TEST(suite, test_str_format);
     SUITE_ADD_TEST(suite, test_sbstring);
     SUITE_ADD_TEST(suite, test_sbs_strcat);
     SUITE_ADD_TEST(suite, test_sbs_substr);