diff --git a/Makefile b/Makefile
index 16a39a04e..f66dbc439 100644
--- a/Makefile
+++ b/Makefile
@@ -145,6 +145,7 @@ include tool/args/args.mk
 include test/tool/args/test.mk
 include third_party/linenoise/linenoise.mk
 include third_party/maxmind/maxmind.mk
+include third_party/double-conversion/double-conversion.mk
 include third_party/lua/lua.mk
 include third_party/make/make.mk
 include third_party/finger/finger.mk
@@ -156,7 +157,6 @@ include third_party/quickjs/quickjs.mk
 include third_party/lz4cli/lz4cli.mk
 include third_party/zip/zip.mk
 include third_party/unzip/unzip.mk
-include third_party/double-conversion/double-conversion.mk
 include tool/build/lib/buildlib.mk
 include third_party/chibicc/chibicc.mk
 include third_party/chibicc/test/test.mk
diff --git a/libc/fmt/atoi.c b/libc/fmt/atoi.c
index e4893db3e..58f3522be 100644
--- a/libc/fmt/atoi.c
+++ b/libc/fmt/atoi.c
@@ -1,5 +1,5 @@
 /*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
-│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+'-'│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
 ╞══════════════════════════════════════════════════════════════════════════════╡
 │ Copyright 2020 Justine Alexandra Roberts Tunney                              │
 │                                                                              │
diff --git a/test/tool/net/lfuncs_test.lua b/test/tool/net/lfuncs_test.lua
index bd414ceff..d4f25f304 100644
--- a/test/tool/net/lfuncs_test.lua
+++ b/test/tool/net/lfuncs_test.lua
@@ -170,5 +170,5 @@ function JsonSerialization()
    EncodeJson({2, 1, 10, 3, "hello"})
 end
 
-print(Benchmark(LuaSerialization), "LuaSerialization")
-print(Benchmark(JsonSerialization), "JsonSerialization")
+print("LuaSerialization", Benchmark(LuaSerialization))
+print("JsonSerialization", Benchmark(JsonSerialization))
diff --git a/test/tool/net/ljson_test.c b/test/tool/net/ljson_test.c
new file mode 100644
index 000000000..e69de29bb
diff --git a/test/tool/net/ljson_test.lua b/test/tool/net/ljson_test.lua
new file mode 100644
index 000000000..e7de68024
--- /dev/null
+++ b/test/tool/net/ljson_test.lua
@@ -0,0 +1,68 @@
+-- Copyright 2022 Justine Alexandra Roberts Tunney
+--
+-- Permission to use, copy, modify, and/or distribute this software for
+-- any purpose with or without fee is hereby granted, provided that the
+-- above copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+-- WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+-- WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+-- AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+-- DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+-- PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+-- TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+assert(EncodeLua(ParseJson[[     ]]) == 'nil')
+assert(EncodeLua(ParseJson[[  0  ]]) ==  '0' )
+assert(EncodeLua(ParseJson[[ [1] ]]) == '{1}')
+assert(EncodeLua(ParseJson[[ 2.3 ]]) == '2.3')
+assert(EncodeLua(ParseJson[[ [1,3,2] ]]) == '{1, 3, 2}')
+assert(EncodeLua(ParseJson[[ {1: 2, 3: 4} ]]) == '{[1]=2, [3]=4}')
+assert(EncodeLua(ParseJson[[ {"foo": 2, "bar": 4} ]]) == '{bar=4, foo=2}')
+assert(EncodeLua(ParseJson[[ -123 ]]) == '-123')
+assert(EncodeLua(ParseJson[[ 1.e6 ]]) == '1000000')
+assert(EncodeLua(ParseJson[[ 1.e-6 ]]) == '1e-06')
+assert(EncodeLua(ParseJson[[ 1e-06 ]]) == '1e-06')
+assert(EncodeLua(ParseJson[[ 9.123e6 ]]) == '9123000')
+assert(EncodeLua(ParseJson[[ [{"heh": [1,3,2]}] ]]) == '{{heh={1, 3, 2}}}')
+assert(EncodeLua(ParseJson[[ 3.14159 ]]) == '3.14159')
+assert(EncodeLua(ParseJson[[ {3=4} ]]) == '{[3]=4}')
+assert(EncodeLua(ParseJson[[ 1e-12 ]]) == '1e-12')
+assert(EncodeJson(ParseJson[[ 1e-12 ]]) == '1e-12')
+
+----------------------------------------------------------------------------------------------------
+-- benchmarks
+
+function JsonParseEmpty()
+   ParseJson[[]]
+end
+
+function JsonParseInt()
+   ParseJson[[ 314159 ]]
+end
+
+function JsonParseDouble()
+   ParseJson[[ 3.14159 ]]
+end
+
+function JsonParseArray()
+   ParseJson[[ [3,1,4,1,5,9] ]]
+end
+
+function JsonParseObject()
+   ParseJson[[ {"3":"1","4":"1","5":"9"} ]]
+end
+
+print('JsonParseEmpty', Benchmark(JsonParseEmpty))
+print('JsonParseInt', Benchmark(JsonParseInt))
+print('JsonParseDouble', Benchmark(JsonParseDouble))
+print('JsonParseArray', Benchmark(JsonParseArray))
+print('JsonParseObject', Benchmark(JsonParseObject))
+
+--			nanos	ticks
+-- JsonParseEmpty	24	77	85	1
+-- JsonParseInt		31	96	82	1
+-- JsonParseDouble	64	199	82	1
+-- JsonParseArray	367	1139	80	1
+-- JsonParseObject	425	1317	79	1
diff --git a/third_party/lua/lua.mk b/third_party/lua/lua.mk
index 22c713a8c..f23af6602 100644
--- a/third_party/lua/lua.mk
+++ b/third_party/lua/lua.mk
@@ -132,6 +132,7 @@ THIRD_PARTY_LUA_A_DIRECTDEPS =						\
 	LIBC_UNICODE							\
 	NET_HTTP							\
 	THIRD_PARTY_LINENOISE						\
+	THIRD_PARTY_DOUBLECONVERSION					\
 	THIRD_PARTY_GDTOA
 
 THIRD_PARTY_LUA_A_DEPS :=						\
diff --git a/third_party/lua/luaencodejsondata.c b/third_party/lua/luaencodejsondata.c
index f3235e981..bb08fe303 100644
--- a/third_party/lua/luaencodejsondata.c
+++ b/third_party/lua/luaencodejsondata.c
@@ -24,7 +24,9 @@
 #include "libc/runtime/gc.internal.h"
 #include "libc/stdio/append.internal.h"
 #include "libc/stdio/strlist.internal.h"
+#include "libc/str/str.h"
 #include "net/http/escape.h"
+#include "third_party/double-conversion/wrapper.h"
 #include "third_party/lua/cosmo.h"
 #include "third_party/lua/lauxlib.h"
 #include "third_party/lua/lua.h"
@@ -38,7 +40,7 @@ static int LuaEncodeJsonDataImpl(lua_State *L, char **buf, int level,
   bool isarray;
   size_t tbllen, i, z;
   struct StrList sl = {0};
-  char ibuf[21], fmt[] = "%.14g";
+  char ibuf[128], fmt[] = "%.14g";
   if (level > 0) {
     switch (lua_type(L, idx)) {
 
@@ -66,22 +68,8 @@ static int LuaEncodeJsonDataImpl(lua_State *L, char **buf, int level,
           RETURN_ON_ERROR(appendd(
               buf, ibuf, FormatInt64(ibuf, luaL_checkinteger(L, idx)) - ibuf));
         } else {
-          // TODO(jart): replace this api
-          while (*numformat == '%' || *numformat == '.' ||
-                 isdigit(*numformat)) {
-            ++numformat;
-          }
-          switch (*numformat) {
-            case 'a':
-            case 'g':
-            case 'f':
-              fmt[4] = *numformat;
-              break;
-            default:
-              // prevent format string hacking
-              goto OnError;
-          }
-          RETURN_ON_ERROR(appendf(buf, fmt, lua_tonumber(L, idx)));
+          RETURN_ON_ERROR(
+              appends(buf, DoubleToEcmascript(ibuf, lua_tonumber(L, idx))));
         }
         return 0;
 
diff --git a/tool/net/help.txt b/tool/net/help.txt
index c6735ad98..820f44e3a 100644
--- a/tool/net/help.txt
+++ b/tool/net/help.txt
@@ -673,6 +673,21 @@ FUNCTIONS
           URIs that do things like embed a PNG file in a web page. See
           encodebase64.c.
 
+  ParseJson(input:str)
+      ├─→ value:*
+      ├─→ true [if useoutput]
+      └─→ nil, error:str
+
+          Turns JSON string into a Lua data structure.
+
+          This is a very permissive parser. That means it should always
+          parse correctly formatted JSON correctly. However it will not
+          complain if the `input` string is weirdly formatted. There is
+          currently no validation performed, other than what we need to
+          ensure security. For example `{3=4}` will decode as `{[3]=4}`
+          even though that structure won't round-trip with `EncodeJson`
+          since redbean won't generate invalid JSON (see Postel's Law).
+
   EncodeJson(value[,options:table])
       ├─→ json:str
       ├─→ true [if useoutput]
diff --git a/tool/net/ljson.c b/tool/net/ljson.c
new file mode 100644
index 000000000..731910468
--- /dev/null
+++ b/tool/net/ljson.c
@@ -0,0 +1,222 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/errno.h"
+#include "libc/limits.h"
+#include "libc/math.h"
+#include "libc/str/str.h"
+#include "libc/str/tpenc.h"
+#include "third_party/lua/lauxlib.h"
+#include "third_party/lua/lua.h"
+
+struct Rc {
+  int t;
+  const char *p;
+};
+
+static int Accumulate(int x, int c, int d) {
+  if (!__builtin_mul_overflow(x, 10, &x) &&
+      !__builtin_add_overflow(x, (c - '0') * d, &x)) {
+    return x;
+  } else {
+    errno = ERANGE;
+    if (d > 0) {
+      return INT_MAX;
+    } else {
+      return INT_MIN;
+    }
+  }
+}
+
+static struct Rc Parse(struct lua_State *L, const char *p, const char *e) {
+  uint64_t w;
+  struct Rc r;
+  luaL_Buffer b;
+  int A, B, C, D;
+  int c, d, i, j, x, y, z;
+  for (d = +1; p < e;) {
+    switch ((c = *p++ & 255)) {
+
+      case '-':
+        d = -1;
+        break;
+
+      case ']':
+      case '}':
+        return (struct Rc){0, p};
+
+      case '[':
+        lua_newtable(L);
+        i = 0;
+        do {
+          r = Parse(L, p, e);
+          p = r.p;
+          if (r.t) {
+            lua_rawseti(L, -2, i++ + 1);
+          }
+        } while (r.t);
+        return (struct Rc){1, p};
+
+      case '{':
+        lua_newtable(L);
+        i = 0;
+        do {
+          r = Parse(L, p, e);
+          p = r.p;
+          if (r.t) {
+            r = Parse(L, p, e);
+            p = r.p;
+            if (!r.t) {
+              lua_pushnil(L);
+            }
+            lua_settable(L, -3);
+          }
+        } while (r.t);
+        return (struct Rc){1, p};
+
+      case '"':
+        luaL_buffinit(L, &b);
+        while (p < e) {
+          switch ((c = *p++ & 255)) {
+            default:
+            AddChar:
+              luaL_addchar(&b, c);
+              break;
+            case '\\':
+              if (p < e) {
+                switch ((c = *p++ & 255)) {
+                  case '"':
+                  case '/':
+                  case '\\':
+                  default:
+                    goto AddChar;
+                  case 'b':
+                    c = '\b';
+                    goto AddChar;
+                  case 'f':
+                    c = '\f';
+                    goto AddChar;
+                  case 'n':
+                    c = '\n';
+                    goto AddChar;
+                  case 'r':
+                    c = '\r';
+                    goto AddChar;
+                  case 't':
+                    c = '\t';
+                    goto AddChar;
+                  case 'u':
+                    if (p + 4 <= e &&                         //
+                        (A = kHexToInt[p[0] & 255]) != -1 &&  //
+                        (B = kHexToInt[p[1] & 255]) != -1 &&  //
+                        (C = kHexToInt[p[2] & 255]) != -1 &&  //
+                        (D = kHexToInt[p[3] & 255]) != -1) {
+                      p += 4;
+                      c = A << 12 | B << 8 | C << 4 | D;
+                      w = tpenc(c);
+                      do {
+                        luaL_addchar(&b, w & 255);
+                      } while ((w >>= 8));
+                      break;
+                    } else {
+                      goto AddChar;
+                    }
+                }
+              }
+              break;
+            case '"':
+              goto FinishString;
+          }
+        }
+      FinishString:
+        luaL_pushresult(&b);
+        return (struct Rc){1, p};
+
+      case '0' ... '9':
+        for (x = (c - '0') * d; p < e; ++p) {
+          c = *p & 255;
+          if (isdigit(c)) {
+            x = Accumulate(x, c, d);
+          } else if (c == '.') {
+            ++p;
+            goto Fraction;
+          } else if (c == 'e' || c == 'E') {
+            ++p;
+            j = 0;
+            y = 0;
+            goto Exponent;
+          } else {
+            break;
+          }
+        }
+        lua_pushinteger(L, x);
+        return (struct Rc){1, p};
+
+      Fraction:
+        for (j = y = 0; p < e; ++p) {
+          c = *p & 255;
+          if (isdigit(c)) {
+            --j;
+            y = Accumulate(y, c, d);
+          } else if (c == 'e' || c == 'E') {
+            ++p;
+            goto Exponent;
+          } else {
+            break;
+          }
+        }
+        lua_pushnumber(L, x + y * exp10(j));
+        return (struct Rc){1, p};
+
+      Exponent:
+        d = +1;
+        for (z = 0; p < e; ++p) {
+          c = *p & 255;
+          if (isdigit(c)) {
+            z = Accumulate(z, c, d);
+          } else if (c == '-') {
+            d = -1;
+          } else if (c == '+') {
+            d = +1;
+          } else {
+            break;
+          }
+        }
+        lua_pushnumber(L, (x + y * exp10(j)) * exp10(z));
+        return (struct Rc){1, p};
+
+      case ',':
+      case ':':
+      case ' ':
+      case '\n':
+      case '\r':
+      case '\t':
+      default:
+        break;
+    }
+  }
+  return (struct Rc){0, p};
+}
+
+/**
+ * Parses JSON data structure string into a Lua data structure.
+ */
+int ParseJson(struct lua_State *L, const char *p, size_t n) {
+  if (n == -1) n = p ? strlen(p) : 0;
+  return Parse(L, p, p + n).t;
+}
diff --git a/tool/net/ljson.h b/tool/net/ljson.h
new file mode 100644
index 000000000..e11b371af
--- /dev/null
+++ b/tool/net/ljson.h
@@ -0,0 +1,11 @@
+#ifndef COSMOPOLITAN_TOOL_NET_LJSON_H_
+#define COSMOPOLITAN_TOOL_NET_LJSON_H_
+#include "third_party/lua/lauxlib.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+int ParseJson(struct lua_State *, const char *, size_t);
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_TOOL_NET_LJSON_H_ */
diff --git a/tool/net/net.mk b/tool/net/net.mk
index fc8f355e5..20821b511 100644
--- a/tool/net/net.mk
+++ b/tool/net/net.mk
@@ -94,6 +94,7 @@ o/$(MODE)/tool/net/redbean.com.dbg:						\
 		o/$(MODE)/tool/net/redbean.o					\
 		o/$(MODE)/tool/net/lfuncs.o					\
 		o/$(MODE)/tool/net/lre.o					\
+		o/$(MODE)/tool/net/ljson.o					\
 		o/$(MODE)/tool/net/lmaxmind.o					\
 		o/$(MODE)/tool/net/lsqlite3.o					\
 		o/$(MODE)/tool/net/largon2.o					\
@@ -212,6 +213,7 @@ o/$(MODE)/tool/net/redbean-demo.com.dbg:					\
 		o/$(MODE)/tool/net/redbean.o					\
 		o/$(MODE)/tool/net/lfuncs.o					\
 		o/$(MODE)/tool/net/lre.o					\
+		o/$(MODE)/tool/net/ljson.o					\
 		o/$(MODE)/tool/net/lmaxmind.o					\
 		o/$(MODE)/tool/net/lsqlite3.o					\
 		o/$(MODE)/tool/net/largon2.o					\
@@ -328,6 +330,7 @@ o/$(MODE)/tool/net/redbean-unsecure.com.dbg:					\
 		o/$(MODE)/tool/net/redbean-unsecure.o				\
 		o/$(MODE)/tool/net/lfuncs.o					\
 		o/$(MODE)/tool/net/lre.o					\
+		o/$(MODE)/tool/net/ljson.o					\
 		o/$(MODE)/tool/net/lmaxmind.o					\
 		o/$(MODE)/tool/net/lsqlite3.o					\
 		o/$(MODE)/tool/net/largon2.o					\
diff --git a/tool/net/redbean.c b/tool/net/redbean.c
index 8167df430..4b235eb57 100644
--- a/tool/net/redbean.c
+++ b/tool/net/redbean.c
@@ -112,6 +112,7 @@
 #include "tool/args/args.h"
 #include "tool/build/lib/case.h"
 #include "tool/net/lfuncs.h"
+#include "tool/net/ljson.h"
 #include "tool/net/luacheck.h"
 #include "tool/net/sandbox.h"
 
@@ -4258,6 +4259,13 @@ static int LuaEncodeLua(lua_State *L) {
   return LuaEncodeSmth(L, LuaEncodeLuaData);
 }
 
+static int LuaParseJson(lua_State *L) {
+  size_t n;
+  const char *p;
+  p = luaL_checklstring(L, 1, &n);
+  return ParseJson(L, p, n);
+}
+
 static int LuaGetUrl(lua_State *L) {
   char *p;
   size_t n;
@@ -5150,6 +5158,7 @@ static const luaL_Reg kLuaFuncs[] = {
     {"ParseHost", LuaParseHost},                                //
     {"ParseHttpDateTime", LuaParseHttpDateTime},                //
     {"ParseIp", LuaParseIp},                                    //
+    {"ParseJson", LuaParseJson},                                //
     {"ParseParams", LuaParseParams},                            //
     {"ParseUrl", LuaParseUrl},                                  //
     {"Popcnt", LuaPopcnt},                                      //