diff --git a/libc/test/src/stdio/scanf_core/CMakeLists.txt b/libc/test/src/stdio/scanf_core/CMakeLists.txt
@@ -30,3 +30,16 @@ add_libc_unittest(
     libc.src.stdio.scanf_core.string_reader
     libc.src.__support.CPP.string_view
 )
+
+add_libc_unittest(
+  converter_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    converter_test.cpp
+  DEPENDS
+    libc.src.stdio.scanf_core.reader
+    libc.src.stdio.scanf_core.string_reader
+    libc.src.stdio.scanf_core.converter
+    libc.src.__support.CPP.string_view
+)
diff --git a/libc/test/src/stdio/scanf_core/converter_test.cpp b/libc/test/src/stdio/scanf_core/converter_test.cpp
@@ -0,0 +1,295 @@
+//===-- Unittests for the basic scanf converters --------------------------===//
+//
+// 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/__support/CPP/string_view.h"
+#include "src/stdio/scanf_core/converter.h"
+#include "src/stdio/scanf_core/core_structs.h"
+#include "src/stdio/scanf_core/reader.h"
+#include "src/stdio/scanf_core/string_reader.h"
+
+#include "utils/UnitTest/Test.h"
+
+TEST(LlvmLibcScanfConverterTest, RawMatchBasic) {
+  const char *str = "abcdef";
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  // Reading "abc" should succeed.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "abc"),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(3));
+
+  // Reading nothing should succeed and not advance.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, ""),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(3));
+
+  // Reading a space where there is none should succeed and not advance.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, " "),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(3));
+
+  // Reading "d" should succeed and advance by 1.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "d"),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(4));
+
+  // Reading "z" should fail and not advance.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "z"),
+            static_cast<int>(__llvm_libc::scanf_core::MATCHING_FAILURE));
+  ASSERT_EQ(reader.chars_read(), size_t(4));
+
+  // Reading "efgh" should fail but advance to the end.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "efgh"),
+            static_cast<int>(__llvm_libc::scanf_core::MATCHING_FAILURE));
+  ASSERT_EQ(reader.chars_read(), size_t(6));
+}
+
+TEST(LlvmLibcScanfConverterTest, RawMatchSpaces) {
+  const char *str = " a \t\n b   cd";
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  // Reading "a" should fail and not advance.
+  // Since there's nothing in the format string (the second argument to
+  // raw_match) to match the space in the buffer it isn't consumed.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "a"),
+            static_cast<int>(__llvm_libc::scanf_core::MATCHING_FAILURE));
+  ASSERT_EQ(reader.chars_read(), size_t(0));
+
+  // Reading "  \t\n  " should succeed and advance past the space.
+  // Any number of space characters in the format string match 0 or more space
+  // characters in the buffer.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "  \t\n  "),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(1));
+
+  // Reading "ab" should fail and only advance past the a
+  // The a characters match, but the format string doesn't have anything to
+  // consume the spaces in the buffer, so it fails.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "ab"),
+            static_cast<int>(__llvm_libc::scanf_core::MATCHING_FAILURE));
+  ASSERT_EQ(reader.chars_read(), size_t(2));
+
+  // Reading "  b" should succeed and advance past the b
+  // Any number of space characters in the format string matches 0 or more space
+  // characters in the buffer.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "  b"),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(7));
+
+  // Reading "\t" should succeed and advance past the spaces to the c
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "\t"),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(10));
+
+  // Reading "c d" should succeed and advance past the d.
+  // Here the space character in the format string is matching 0 space
+  // characters in the buffer.
+  ASSERT_EQ(__llvm_libc::scanf_core::raw_match(&reader, "c d"),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(12));
+}
+
+TEST(LlvmLibcScanfConverterTest, StringConvSimple) {
+  const char *str = "abcDEF123 654LKJihg";
+  char result[20];
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  __llvm_libc::scanf_core::FormatSection conv;
+  conv.has_conv = true;
+  conv.conv_name = 's';
+  conv.output_ptr = result;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(9));
+  ASSERT_STREQ(result, "abcDEF123");
+
+  //%s skips all spaces before beginning to read.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(19));
+  ASSERT_STREQ(result, "654LKJihg");
+}
+
+TEST(LlvmLibcScanfConverterTest, StringConvNoWrite) {
+  const char *str = "abcDEF123 654LKJihg";
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  __llvm_libc::scanf_core::FormatSection conv;
+  conv.has_conv = true;
+  conv.conv_name = 's';
+  conv.flags = __llvm_libc::scanf_core::NO_WRITE;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(9));
+
+  //%s skips all spaces before beginning to read.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(19));
+}
+
+TEST(LlvmLibcScanfConverterTest, StringConvWidth) {
+  const char *str = "abcDEF123 654LKJihg";
+  char result[6];
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  __llvm_libc::scanf_core::FormatSection conv;
+  conv.has_conv = true;
+  conv.conv_name = 's';
+  conv.max_width = 5; // this means the result takes up 6 characters (with \0).
+  conv.output_ptr = result;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(5));
+  ASSERT_STREQ(result, "abcDE");
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(9));
+  ASSERT_STREQ(result, "F123");
+
+  //%s skips all spaces before beginning to read.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(15));
+  ASSERT_STREQ(result, "654LK");
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(19));
+  ASSERT_STREQ(result, "Jihg");
+}
+
+TEST(LlvmLibcScanfConverterTest, CharsConv) {
+  const char *str = "abcDEF123 654LKJihg MNOpqr&*(";
+  char result[20];
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  __llvm_libc::scanf_core::FormatSection conv;
+  conv.has_conv = true;
+  conv.conv_name = 'c';
+  conv.output_ptr = result;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(1));
+  ASSERT_EQ(result[0], 'a');
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(2));
+  ASSERT_EQ(result[0], 'b');
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(3));
+  ASSERT_EQ(result[0], 'c');
+
+  // Switch from character by character to 8 at a time.
+  conv.max_width = 8;
+  __llvm_libc::cpp::string_view result_view(result, 8);
+
+  //%c doesn't stop on spaces.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(11));
+  ASSERT_EQ(result_view, __llvm_libc::cpp::string_view("DEF123 6", 8));
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(19));
+  ASSERT_EQ(result_view, __llvm_libc::cpp::string_view("54LKJihg", 8));
+
+  //%c also doesn't skip spaces at the start.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(27));
+  ASSERT_EQ(result_view, __llvm_libc::cpp::string_view(" MNOpqr&", 8));
+
+  //%c will stop on a null byte though.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(29));
+  ASSERT_EQ(__llvm_libc::cpp::string_view(result, 2),
+            __llvm_libc::cpp::string_view("*(", 2));
+}
+
+TEST(LlvmLibcScanfConverterTest, ScansetConv) {
+  const char *str = "abcDEF[123] 654LKJihg";
+  char result[20];
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  __llvm_libc::scanf_core::FormatSection conv;
+  conv.has_conv = true;
+  conv.conv_name = '[';
+  conv.output_ptr = result;
+
+  __llvm_libc::cpp::bitset<256> bitset1;
+  bitset1.set_range('a', 'c');
+  bitset1.set_range('D', 'F');
+  bitset1.set_range('1', '6');
+  bitset1.set('[');
+  bitset1.set(']');
+
+  conv.scan_set = bitset1;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(11));
+  ASSERT_EQ(__llvm_libc::cpp::string_view(result, 11),
+            __llvm_libc::cpp::string_view("abcDEF[123]", 11));
+
+  // The scanset conversion doesn't consume leading spaces. If it did it would
+  // return "654" here.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::MATCHING_FAILURE));
+  ASSERT_EQ(reader.chars_read(), size_t(11));
+
+  // This set is everything except for a-g.
+  __llvm_libc::cpp::bitset<256> bitset2;
+  bitset2.set_range('a', 'g');
+  bitset2.flip();
+  conv.scan_set = bitset2;
+
+  conv.max_width = 5;
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(16));
+  ASSERT_EQ(__llvm_libc::cpp::string_view(result, 5),
+            __llvm_libc::cpp::string_view(" 654L", 5));
+
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(20));
+  ASSERT_EQ(__llvm_libc::cpp::string_view(result, 4),
+            __llvm_libc::cpp::string_view("KJih", 4));
+
+  // This set is g and '\0'.
+  __llvm_libc::cpp::bitset<256> bitset3;
+  bitset3.set('g');
+  bitset3.set('\0');
+  conv.scan_set = bitset3;
+
+  // Even though '\0' is in the scanset, it should still stop on it.
+  ASSERT_EQ(__llvm_libc::scanf_core::convert(&reader, conv),
+            static_cast<int>(__llvm_libc::scanf_core::READ_OK));
+  ASSERT_EQ(reader.chars_read(), size_t(21));
+  ASSERT_EQ(__llvm_libc::cpp::string_view(result, 1),
+            __llvm_libc::cpp::string_view("g", 1));
+}