diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -33,6 +33,7 @@
     libc.src.string.bcmp
     libc.src.string.bcopy
     libc.src.string.bzero
+    libc.src.string.index
     libc.src.string.memccpy
     libc.src.string.memchr
     libc.src.string.memcmp
@@ -41,6 +42,7 @@
     libc.src.string.mempcpy
     libc.src.string.memrchr
     libc.src.string.memset
+    libc.src.string.rindex
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcasecmp
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -24,6 +24,7 @@
     libc.src.string.bcmp
     libc.src.string.bcopy
     libc.src.string.bzero
+    libc.src.string.index
     libc.src.string.memccpy
     libc.src.string.memchr
     libc.src.string.memcmp
@@ -32,6 +33,7 @@
     libc.src.string.mempcpy
     libc.src.string.memrchr
     libc.src.string.memset
+    libc.src.string.rindex
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcasecmp
diff --git a/libc/config/linux/riscv64/entrypoints.txt b/libc/config/linux/riscv64/entrypoints.txt
--- a/libc/config/linux/riscv64/entrypoints.txt
+++ b/libc/config/linux/riscv64/entrypoints.txt
@@ -33,6 +33,7 @@
     libc.src.string.bcmp
     libc.src.string.bcopy
     libc.src.string.bzero
+    libc.src.string.index
     libc.src.string.memccpy
     libc.src.string.memchr
     libc.src.string.memcmp
@@ -41,6 +42,7 @@
     libc.src.string.mempcpy
     libc.src.string.memrchr
     libc.src.string.memset
+    libc.src.string.rindex
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcasecmp
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -33,6 +33,7 @@
     libc.src.string.bcmp
     libc.src.string.bcopy
     libc.src.string.bzero
+    libc.src.string.index
     libc.src.string.memccpy
     libc.src.string.memchr
     libc.src.string.memcmp
@@ -41,6 +42,7 @@
     libc.src.string.mempcpy
     libc.src.string.memrchr
     libc.src.string.memset
+    libc.src.string.rindex
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcasecmp
diff --git a/libc/spec/bsd_ext.td b/libc/spec/bsd_ext.td
--- a/libc/spec/bsd_ext.td
+++ b/libc/spec/bsd_ext.td
@@ -39,6 +39,16 @@
             RetValSpec<IntType>,
             [ArgSpec<ConstCharPtr>, ArgSpec<ConstCharPtr>, ArgSpec<SizeTType>]
         >,
+        FunctionSpec<
+            "index",
+            RetValSpec<CharPtr>,
+            [ArgSpec<ConstCharPtr>, ArgSpec<IntType>]
+        >,
+        FunctionSpec<
+            "rindex",
+            RetValSpec<CharPtr>,
+            [ArgSpec<ConstCharPtr>, ArgSpec<IntType>]
+        >,
       ]
   >;
 
diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
--- a/libc/src/string/CMakeLists.txt
+++ b/libc/src/string/CMakeLists.txt
@@ -31,6 +31,16 @@
     bcopy.h
 )
 
+add_entrypoint_object(
+  index
+  SRCS
+    index.cpp
+  HDRS
+    index.h
+  DEPENDS
+    .memory_utils.strchr_implementation
+)
+
 add_entrypoint_object(
   memccpy
   SRCS
@@ -67,6 +77,16 @@
     memrchr.h
 )
 
+add_entrypoint_object(
+  rindex
+  SRCS
+    rindex.cpp
+  HDRS
+    rindex.h
+  DEPENDS
+    .memory_utils.strchr_implementation
+)
+
 add_entrypoint_object(
   stpcpy
   SRCS
diff --git a/libc/src/string/index.h b/libc/src/string/index.h
new file mode 100644
--- /dev/null
+++ b/libc/src/string/index.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for index -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STRING_INDEX_H
+#define LLVM_LIBC_SRC_STRING_INDEX_H
+
+namespace __llvm_libc {
+
+char *index(const char *src, int c);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_INDEX_H
diff --git a/libc/src/string/index.cpp b/libc/src/string/index.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/string/index.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of index -------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/string/index.h"
+
+#include "src/__support/common.h"
+#include "src/string/memory_utils/strchr_implementations.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(char *, index, (const char *src, int c)) {
+  return strchr_implementation(src, c);
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/string/rindex.h b/libc/src/string/rindex.h
new file mode 100644
--- /dev/null
+++ b/libc/src/string/rindex.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for rindex ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STRING_RINDEX_H
+#define LLVM_LIBC_SRC_STRING_RINDEX_H
+
+namespace __llvm_libc {
+
+char *rindex(const char *src, int c);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_RINDEX_H
diff --git a/libc/src/string/rindex.cpp b/libc/src/string/rindex.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/string/rindex.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of rindex ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/string/rindex.h"
+
+#include "src/__support/common.h"
+#include "src/string/memory_utils/strchr_implementations.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(char *, rindex, (const char *src, int c)) {
+  return strrchr_implementation(src, c);
+}
+
+} // namespace __llvm_libc
diff --git a/libc/test/src/string/CMakeLists.txt b/libc/test/src/string/CMakeLists.txt
--- a/libc/test/src/string/CMakeLists.txt
+++ b/libc/test/src/string/CMakeLists.txt
@@ -14,6 +14,23 @@
     LibcMemoryHelpers
 )
 
+add_header_library(
+  strchr_test_support
+  HDRS
+    StrchrTest.h
+)
+
+add_libc_unittest(
+  index_test
+  SUITE
+    libc_string_unittests
+  SRCS
+    index_test.cpp
+  DEPENDS
+    libc.src.string.index
+    .strchr_test_support
+)
+
 add_libc_unittest(
   memccpy_test
   SUITE
@@ -54,6 +71,17 @@
     libc.src.string.memrchr
 )
 
+add_libc_unittest(
+  rindex_test
+  SUITE
+    libc_string_unittests
+  SRCS
+    rindex_test.cpp
+  DEPENDS
+    libc.src.string.rindex
+    .strchr_test_support
+)
+
 add_libc_unittest(
   stpcpy_test
   SUITE
@@ -84,12 +112,6 @@
     libc.src.string.strcat
 )
 
-add_header_library(
-  strchr_test_support
-  HDRS
-    StrchrTest.h
-)
-
 add_libc_unittest(
   strchr_test
   SUITE
diff --git a/libc/test/src/string/index_test.cpp b/libc/test/src/string/index_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/string/index_test.cpp
@@ -0,0 +1,14 @@
+//===-- Unittests for index -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "StrchrTest.h"
+
+#include "src/string/index.h"
+#include "test/UnitTest/Test.h"
+
+STRCHR_TEST(Index, __llvm_libc::index)
diff --git a/libc/test/src/string/rindex_test.cpp b/libc/test/src/string/rindex_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/string/rindex_test.cpp
@@ -0,0 +1,14 @@
+//===-- Unittests for rindex ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "StrchrTest.h"
+
+#include "src/string/rindex.h"
+#include "test/UnitTest/Test.h"
+
+STRRCHR_TEST(Rindex, __llvm_libc::rindex)