diff --git a/MANIFEST b/MANIFEST
index 419e5ee45..f3b952e08 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -100,8 +100,14 @@ lib/iolog/Makefile.in
 lib/iolog/hostcheck.c
 lib/iolog/iolog_fileio.c
 lib/iolog/iolog_json.c
+lib/iolog/iolog_json.h
 lib/iolog/iolog_path.c
 lib/iolog/iolog_util.c
+lib/iolog/regress/iolog_json/check_iolog_json.c
+lib/iolog/regress/iolog_json/test1.in
+lib/iolog/regress/iolog_json/test2.in
+lib/iolog/regress/iolog_json/test2.out.ok
+lib/iolog/regress/iolog_json/test3.in
 lib/iolog/regress/iolog_path/check_iolog_path.c
 lib/iolog/regress/iolog_path/data
 lib/iolog/regress/iolog_util/check_iolog_util.c
diff --git a/lib/iolog/Makefile.in b/lib/iolog/Makefile.in
index 9c458b4ed..105332020 100644
--- a/lib/iolog/Makefile.in
+++ b/lib/iolog/Makefile.in
@@ -75,7 +75,7 @@ PVS_IGNORE = 'V707,V011,V002,V536'
 PVS_LOG_OPTS = -a 'GA:1,2' -e -t errorfile -d $(PVS_IGNORE)
 
 # Regression tests
-TEST_PROGS = check_iolog_path check_iolog_util
+TEST_PROGS = check_iolog_json check_iolog_path check_iolog_util
 TEST_LIBS = @LIBS@
 TEST_LDFLAGS = @LDFLAGS@
 
@@ -97,6 +97,8 @@ CHECK_IOLOG_PATH_OBJS = check_iolog_path.lo iolog_path.lo
 
 CHECK_IOLOG_UTIL_OBJS = check_iolog_util.lo iolog_json.lo iolog_util.lo
 
+CHECK_IOLOG_JSON_OBJS = check_iolog_json.lo iolog_json.lo
+
 all: libsudo_iolog.la
 
 pvs-log-files: $(POBJS)
@@ -132,6 +134,9 @@ check_iolog_path: $(CHECK_IOLOG_PATH_OBJS) libsudo_iolog.la
 check_iolog_util: $(CHECK_IOLOG_UTIL_OBJS) libsudo_iolog.la
 	$(LIBTOOL) $(LTFLAGS) --mode=link $(CC) -o $@ $(CHECK_IOLOG_UTIL_OBJS) libsudo_iolog.la $(ASAN_LDFLAGS) $(PIE_LDFLAGS) $(SSP_LDFLAGS) $(TEST_LDFLAGS) $(TEST_LIBS)
 
+check_iolog_json: $(CHECK_IOLOG_JSON_OBJS) libsudo_iolog.la
+	$(LIBTOOL) $(LTFLAGS) --mode=link $(CC) -o $@ $(CHECK_IOLOG_JSON_OBJS) libsudo_iolog.la $(ASAN_LDFLAGS) $(PIE_LDFLAGS) $(SSP_LDFLAGS) $(TEST_LDFLAGS) $(TEST_LIBS)
+
 pre-install:
 
 install:
@@ -159,6 +164,7 @@ check: $(TEST_PROGS)
 	    LC_ALL=C; export LC_ALL; \
 	    unset LANG || LANG=; \
 	    rval=0; \
+	    ./check_iolog_json $(srcdir)/regress/iolog_json/*.in || rval=`expr $$rval + $$?`; \
 	    ./check_iolog_path $(srcdir)/regress/iolog_path/data || rval=`expr $$rval + $$?`; \
 	    ./check_iolog_util || rval=`expr $$rval + $$?`; \
 	    exit $$rval; \
@@ -182,6 +188,20 @@ realclean: distclean
 cleandir: realclean
 
 # Autogenerated dependencies, do not modify
+check_iolog_json.lo: $(srcdir)/regress/iolog_json/check_iolog_json.c \
+                     $(incdir)/compat/stdbool.h $(incdir)/sudo_compat.h \
+                     $(incdir)/sudo_fatal.h $(incdir)/sudo_json.h \
+                     $(incdir)/sudo_queue.h $(incdir)/sudo_util.h \
+                     $(srcdir)/iolog_json.h $(top_builddir)/config.h
+	$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(ASAN_CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/regress/iolog_json/check_iolog_json.c
+check_iolog_json.i: $(srcdir)/regress/iolog_json/check_iolog_json.c \
+                     $(incdir)/compat/stdbool.h $(incdir)/sudo_compat.h \
+                     $(incdir)/sudo_fatal.h $(incdir)/sudo_json.h \
+                     $(incdir)/sudo_queue.h $(incdir)/sudo_util.h \
+                     $(srcdir)/iolog_json.h $(top_builddir)/config.h
+	$(CC) -E -o $@ $(CPPFLAGS) $<
+check_iolog_json.plog: check_iolog_json.i
+	rm -f $@; pvs-studio --cfg $(PVS_CFG) --sourcetree-root $(top_srcdir) --skip-cl-exe yes --source-file $(srcdir)/regress/iolog_json/check_iolog_json.c --i-file $< --output-file $@
 check_iolog_path.lo: $(srcdir)/regress/iolog_path/check_iolog_path.c \
                      $(incdir)/compat/stdbool.h $(incdir)/sudo_compat.h \
                      $(incdir)/sudo_fatal.h $(incdir)/sudo_iolog.h \
@@ -241,14 +261,14 @@ iolog_json.lo: $(srcdir)/iolog_json.c $(incdir)/compat/stdbool.h \
                $(incdir)/sudo_fatal.h $(incdir)/sudo_gettext.h \
                $(incdir)/sudo_iolog.h $(incdir)/sudo_json.h \
                $(incdir)/sudo_queue.h $(incdir)/sudo_util.h \
-               $(top_builddir)/config.h
+               $(srcdir)/iolog_json.h $(top_builddir)/config.h
 	$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(ASAN_CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/iolog_json.c
 iolog_json.i: $(srcdir)/iolog_json.c $(incdir)/compat/stdbool.h \
                $(incdir)/sudo_compat.h $(incdir)/sudo_debug.h \
                $(incdir)/sudo_fatal.h $(incdir)/sudo_gettext.h \
                $(incdir)/sudo_iolog.h $(incdir)/sudo_json.h \
                $(incdir)/sudo_queue.h $(incdir)/sudo_util.h \
-               $(top_builddir)/config.h
+               $(srcdir)/iolog_json.h $(top_builddir)/config.h
 	$(CC) -E -o $@ $(CPPFLAGS) $<
 iolog_json.plog: iolog_json.i
 	rm -f $@; pvs-studio --cfg $(PVS_CFG) --sourcetree-root $(top_srcdir) --skip-cl-exe yes --source-file $(srcdir)/iolog_json.c --i-file $< --output-file $@
diff --git a/lib/iolog/iolog_json.c b/lib/iolog/iolog_json.c
index 4372d0b20..021073be6 100644
--- a/lib/iolog/iolog_json.c
+++ b/lib/iolog/iolog_json.c
@@ -49,31 +49,10 @@
 #include "sudo_compat.h"
 #include "sudo_fatal.h"
 #include "sudo_debug.h"
-#include "sudo_queue.h"
-#include "sudo_json.h"
 #include "sudo_util.h"
 #include "sudo_iolog.h"
 
-TAILQ_HEAD(json_item_list, json_item);
-
-struct json_object {
-    struct json_item *parent;
-    struct json_item_list items;
-};
-
-struct json_item {
-    TAILQ_ENTRY(json_item) entries;
-    char *name;		/* may be NULL for first brace */
-    unsigned int lineno;
-    enum json_value_type type;
-    union {
-	struct json_object child;
-	char *string;
-	long long number;
-	id_t id;
-	bool boolean;
-    } u;
-};
+#include "iolog_json.h"
 
 struct json_stack {
     unsigned int depth;
@@ -128,7 +107,7 @@ json_store_lines(struct json_item *item, struct iolog_info *li)
     debug_return_bool(true);
 }
 
-static char **
+char **
 json_array_to_strvec(struct json_object *array)
 {
     struct json_item *item;
@@ -137,6 +116,7 @@ json_array_to_strvec(struct json_object *array)
     debug_decl(json_array_to_strvec, SUDO_DEBUG_UTIL);
 
     TAILQ_FOREACH(item, &array->items, entries) {
+	/* Can only convert arrays of string. */
 	if (item->type != JSON_STRING) {
 	    sudo_warnx(U_("expected JSON_STRING, got %d"), item->type);
 	    debug_return_ptr(NULL);
@@ -380,7 +360,7 @@ json_parse_string(char **strp)
     debug_return_str(ret);
 }
 
-static void
+void
 free_json_items(struct json_item_list *items)
 {
     struct json_item *item;
@@ -498,6 +478,19 @@ json_insert_bool(struct json_item_list *items, char *name, bool value,
     debug_return_bool(true);
 }
 
+static bool
+json_insert_null(struct json_item_list *items, char *name, unsigned int lineno)
+{
+    struct json_item *item;
+    debug_decl(json_insert_null, SUDO_DEBUG_UTIL);
+
+    if ((item = new_json_item(JSON_NULL, name, lineno)) == NULL)
+	debug_return_bool(false);
+    TAILQ_INSERT_TAIL(items, item, entries);
+
+    debug_return_bool(true);
+}
+
 static bool
 json_insert_num(struct json_item_list *items, char *name, long long value,
     unsigned int lineno)
@@ -557,10 +550,9 @@ json_stack_push(struct json_stack *stack, struct json_item_list *items,
 }
 
 bool
-iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
+iolog_parse_json(FILE *fp, const char *filename, struct json_object *root)
 {
-    struct json_object root = { NULL, TAILQ_HEAD_INITIALIZER(root.items) };
-    struct json_object *curobj = &root;
+    struct json_object *curobj = root;
     struct json_object *curarray = NULL;
     struct json_stack objstack = JSON_STACK_INTIALIZER(objstack);
     struct json_stack arrstack = JSON_STACK_INTIALIZER(arrstack);
@@ -569,9 +561,13 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
     char *buf = NULL;
     size_t bufsize = 0;
     ssize_t len;
-    long long num;
     bool ret = false;
-    debug_decl(iolog_parse_loginfo_json, SUDO_DEBUG_UTIL);
+    long long num;
+    char ch;
+    debug_decl(iolog_parse_json, SUDO_DEBUG_UTIL);
+
+    root->parent = NULL;
+    TAILQ_INIT(&root->items);
 
     while ((len = getdelim(&buf, &bufsize, '\n', fp)) != -1) {
 	char *cp = buf;
@@ -625,8 +621,13 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 		    sudo_warnx(U_("unexpected array"));
 		    goto parse_error;
 		}
-		curarray = json_stack_push(&arrstack, &curobj->items, curarray,
-		    JSON_ARRAY, name, lineno);
+		if (curarray != NULL) {
+		    curarray = json_stack_push(&arrstack, &curarray->items,
+			curarray, JSON_ARRAY, name, lineno);
+		} else {
+		    curarray = json_stack_push(&arrstack, &curobj->items,
+			NULL, JSON_ARRAY, name, lineno);
+		}
 		if (curarray == NULL)
 		    goto parse_error;
 		name = NULL;
@@ -666,13 +667,15 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 		}
 		break;
 	    case 't':
-		if (name == NULL) {
+		if (name == NULL && curarray == NULL) {
 		    sudo_warnx(U_("unexpected boolean"));
 		    goto parse_error;
 		}
-		if (strcmp(cp, "true") != 0)
+		if (strncmp(cp, "true", sizeof("true") - 1) != 0)
 		    goto parse_error;
 		cp += sizeof("true") - 1;
+		if (*cp != ',' && !isspace((unsigned char)*cp) && *cp != '\0')
+		    goto parse_error;
 
 		if (curarray != NULL) {
 		    if (!json_insert_bool(&curarray->items, NULL, true, lineno))
@@ -684,13 +687,15 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 		}
 		break;
 	    case 'f':
-		if (name == NULL) {
+		if (name == NULL && curarray == NULL) {
 		    sudo_warnx(U_("unexpected boolean"));
 		    goto parse_error;
 		}
-		if (strcmp(cp, "false") != 0)
+		if (strncmp(cp, "false", sizeof("false") - 1) != 0)
 		    goto parse_error;
 		cp += sizeof("false") - 1;
+		if (*cp != ',' && !isspace((unsigned char)*cp) && *cp != '\0')
+		    goto parse_error;
 
 		if (curarray != NULL) {
 		    if (!json_insert_bool(&curarray->items, NULL, false, lineno))
@@ -702,16 +707,34 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 		}
 		break;
 	    case 'n':
-		if (strcmp(cp, "null") == 0)
-		    sudo_warnx(U_("null not allowed"));
-		goto parse_error;
+		if (name == NULL && curarray == NULL) {
+		    sudo_warnx(U_("unexpected boolean"));
+		    goto parse_error;
+		}
+		if (strncmp(cp, "null", sizeof("null") - 1) != 0)
+		    goto parse_error;
+		cp += sizeof("null") - 1;
+		if (*cp != ',' && !isspace((unsigned char)*cp) && *cp != '\0')
+		    goto parse_error;
+
+		if (curarray != NULL) {
+		    if (!json_insert_null(&curarray->items, NULL, lineno))
+			goto parse_error;
+		} else {
+		    if (!json_insert_null(&curobj->items, name, lineno))
+			goto parse_error;
+		    name = NULL;
+		}
+		break;
 	    case '+': case '-': case '0': case '1': case '2': case '3':
 	    case '4': case '5': case '6': case '7': case '8': case '9':
-		if (name == NULL) {
+		if (name == NULL && curarray == NULL) {
 		    sudo_warnx(U_("unexpected number"));
 		    goto parse_error;
 		}
-		len = strcspn(cp, " \t\r\n,");
+		/* XXX - strtonumx() would be simpler here. */
+		len = strcspn(cp, " \f\n\r\t\v,");
+		ch = cp[len];
 		cp[len] = '\0';
 		num = sudo_strtonum(cp, LLONG_MIN, LLONG_MAX, &errstr);
 		if (errstr != NULL) {
@@ -719,6 +742,7 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 		    goto parse_error;
 		}
 		cp += len;
+		*cp = ch;
 
 		if (curarray != NULL) {
 		    if (!json_insert_num(&curarray->items, NULL, num, lineno))
@@ -743,18 +767,34 @@ iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
 	goto parse_error;
     }
 
-    /* Walk the stack and parse entries. */
-    ret = iolog_parse_json_object(&root, li);
-
+    ret = true;
     goto done;
 
 parse_error:
-    sudo_warnx(U_("%s/%s:%u unable to parse \"%s\""), iolog_dir,
-	"log.json", lineno, buf);
+    sudo_warnx(U_("%s:%u unable to parse \"%s\""), filename, lineno, buf);
 done:
     free(buf);
     free(name);
-    free_json_items(&root.items);
+    if (!ret)
+	free_json_items(&root->items);
+
+    debug_return_bool(ret);
+}
+
+bool
+iolog_parse_loginfo_json(FILE *fp, const char *iolog_dir, struct iolog_info *li)
+{
+    struct json_object root;
+    bool ret = false;
+    debug_decl(iolog_parse_loginfo_json, SUDO_DEBUG_UTIL);
+
+    if (iolog_parse_json(fp, iolog_dir, &root)) {
+	/* Walk the stack and parse entries. */
+	ret = iolog_parse_json_object(&root, li);
+
+	/* Cleanup. */
+	free_json_items(&root.items);
+    }
 
     debug_return_bool(ret);
 }
diff --git a/lib/iolog/iolog_json.h b/lib/iolog/iolog_json.h
new file mode 100644
index 000000000..bc28dfa3e
--- /dev/null
+++ b/lib/iolog/iolog_json.h
@@ -0,0 +1,50 @@
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2020 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * Permission to use, copy, modify, and 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.
+ */
+
+#ifndef IOLOG_JSON_H
+#define IOLOG_JSON_H
+
+#include "sudo_json.h"
+#include "sudo_queue.h"
+
+TAILQ_HEAD(json_item_list, json_item);
+
+struct json_object {
+    struct json_item *parent;
+    struct json_item_list items;
+};
+
+struct json_item {
+    TAILQ_ENTRY(json_item) entries;
+    char *name;		/* may be NULL for first brace */
+    unsigned int lineno;
+    enum json_value_type type;
+    union {
+	struct json_object child;
+	char *string;
+	long long number;
+	id_t id;
+	bool boolean;
+    } u;
+};
+
+void free_json_items(struct json_item_list *items);
+bool iolog_parse_json(FILE *fp, const char *filename, struct json_object *root);
+char **json_array_to_strvec(struct json_object *array);
+
+#endif /* IOLOG_JSON_H */
diff --git a/lib/iolog/regress/iolog_json/check_iolog_json.c b/lib/iolog/regress/iolog_json/check_iolog_json.c
new file mode 100644
index 000000000..b7673ecbb
--- /dev/null
+++ b/lib/iolog/regress/iolog_json/check_iolog_json.c
@@ -0,0 +1,271 @@
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2020 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * Permission to use, copy, modify, and 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 <config.h>
+
+#include <sys/types.h>
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef HAVE_STRING_H
+# include <string.h>
+#endif /* HAVE_STRING_H */
+#ifdef HAVE_STRINGS_H
+# include <strings.h>
+#endif /* HAVE_STRINGS_H */
+#include <limits.h>
+#include <unistd.h>
+
+#define SUDO_ERROR_WRAP 0
+
+#include "sudo_compat.h"
+#include "sudo_util.h"
+#include "sudo_fatal.h"
+
+#include "iolog_json.h"
+
+__dso_public int main(int argc, char *argv[]);
+
+bool
+json_print_object(struct json_container *json, struct json_object *object)
+{
+    struct json_item *item;
+    struct json_value json_value;
+    bool ret = false;
+
+    TAILQ_FOREACH(item, &object->items, entries) {
+	switch (item->type) {
+	case JSON_STRING:
+	    json_value.type = JSON_STRING;
+	    json_value.u.string = item->u.string;
+	    if (!sudo_json_add_value(json, item->name, &json_value))
+		goto oom;
+	    break;
+	case JSON_NUMBER:
+	    json_value.type = JSON_NUMBER;
+	    json_value.u.number = item->u.number;
+	    if (!sudo_json_add_value(json, item->name, &json_value))
+		goto oom;
+	    break;
+	case JSON_OBJECT:
+	    if (!sudo_json_open_object(json, item->name))
+		goto oom;
+	    if (!json_print_object(json, &item->u.child))
+		goto done;
+	    if (!sudo_json_close_object(json))
+		goto oom;
+	    break;
+	case JSON_ARRAY:
+	    if (!sudo_json_open_array(json, item->name))
+		goto oom;
+	    if (!json_print_object(json, &item->u.child))
+		goto done;
+	    if (!sudo_json_close_array(json))
+		goto oom;
+	    break;
+	case JSON_BOOL:
+	    json_value.type = JSON_BOOL;
+	    json_value.u.boolean = item->u.boolean;
+	    if (!sudo_json_add_value(json, item->name, &json_value))
+		goto oom;
+	    break;
+	case JSON_NULL:
+	    json_value.type = JSON_NULL;
+	    if (!sudo_json_add_value(json, item->name, &json_value))
+		goto oom;
+	    break;
+	default:
+	    sudo_warnx("unsupported JSON type %d", item->type);
+	    goto done;
+	}
+    }
+
+    ret = true;
+    goto done;
+
+oom:
+    sudo_warnx("%s: %s", __func__, "unable to allocate memory");
+done:
+    return ret;
+}
+
+static bool
+json_format(struct json_container *json, struct json_object *object)
+{
+    struct json_item *item;
+    bool ret = false;
+
+    /* First object holds all the actual data. */
+    item = TAILQ_FIRST(&object->items);
+    if (item->type != JSON_OBJECT) {
+	sudo_warnx("expected JSON_OBJECT, got %d", item->type);
+	goto done;
+    }
+    object = &item->u.child;
+
+    if (!json_print_object(json, object))
+	goto done;
+
+    ret = true;
+
+done:
+    return ret;
+}
+
+static void
+usage(void)
+{
+    fprintf(stderr, "usage: %s [-c] input_file ...\n",
+	getprogname());
+    exit(EXIT_FAILURE);
+}
+
+static bool
+compare(FILE *fp, const char *infile, struct json_container *json)
+{
+    const char *cp;
+    unsigned int lineno = 0;
+    size_t linesize = 0;
+    char *line = NULL;
+    ssize_t len;
+
+    cp = sudo_json_get_buf(json);
+
+    while ((len = getdelim(&line, &linesize, '\n', fp)) != -1) {
+	lineno++;
+
+	/* skip open/close brace, not present in formatted output */
+	if (lineno == 1 && strcmp(line, "{\n") == 0)
+	    continue;
+	if (*cp == '\0' && strcmp(line, "}\n") == 0)
+	    continue;
+
+	/* Ignore newlines in output to make comparison easier. */
+	if (*cp == '\n')
+	    cp++;
+	if (line[len - 1] == '\n')
+	    len--;
+
+	if (strncmp(line, cp, len) != 0) {
+	    fprintf(stderr, "%s: mismatch on line %u\n", infile, lineno);
+	    fprintf(stderr, "expected: %s", line);
+	    fprintf(stderr, "got     : %.*s\n", (int)len, cp);
+	    return false;
+	}
+	cp += len;
+    }
+    free(line);
+
+    return true;
+}
+
+int
+main(int argc, char *argv[])
+{
+    struct json_object root;
+    int ch, i, tests = 0, errors = 0;
+    bool cat = false;
+
+    initprogname(argc > 0 ? argv[0] : "check_iolog_json");
+
+    while ((ch = getopt(argc, argv, "c")) != -1) {
+	switch (ch) {
+	    case 'c':
+		cat = true;
+		break;
+	    default:
+		usage();
+	}
+    }
+    argc -= optind;
+    argv += optind;
+
+    if (argc < 1)
+	usage();
+
+    for (i = 0; i < argc; i++) {
+	struct json_container json;
+	const char *infile = argv[i];
+	const char *outfile = argv[i];
+	const char *cp;
+	char pathbuf[PATH_MAX];
+	FILE *infp = NULL;
+	FILE *outfp = NULL;
+
+	tests++;
+
+	if (!sudo_json_init(&json, 4, false, true)) {
+	    errors++;
+	    continue;
+	}
+
+	/* Parse input file. */
+	if ((infp = fopen(infile, "r")) == NULL) {
+	    sudo_warn("%s", argv[1]);
+	    errors++;
+	    goto next;
+	}
+	if (!iolog_parse_json(infp, infile, &root)) {
+	    errors++;
+	    goto next;
+	}
+
+	/* Format as pretty-printed JSON */
+	if (!json_format(&json, &root)) {
+	    errors++;
+	    goto next;
+	}
+
+	/* Check for a .out.ok file in the same location as the .in file. */
+	cp = strrchr(infile, '.');
+	if (cp != NULL && strcmp(cp, ".in") == 0) {
+	    snprintf(pathbuf, sizeof(pathbuf), "%.*s.out.ok",
+		(int)(cp - infile), infile);
+	    if ((outfp = fopen(pathbuf, "r")) != NULL)
+		outfile = pathbuf;
+	}
+	if (outfp == NULL)
+	    outfp = infp;
+
+	/* Compare output to expected output. */
+	rewind(outfp);
+	if (!compare(outfp, outfile, &json))
+	    errors++;
+
+	/* Write the formatted output to stdout for -c (cat) */
+	if (cat) {
+	    fprintf(stdout, "{%s\n}\n", sudo_json_get_buf(&json));
+	    fflush(stdout);
+	}
+
+next:
+	free_json_items(&root.items);
+	sudo_json_free(&json);
+	if (infp != NULL)
+	    fclose(infp);
+	if (outfp != NULL && outfp != infp)
+	    fclose(outfp);
+    }
+
+    if (tests != 0) {
+	printf("iolog_json: %d test%s run, %d errors, %d%% success rate\n",
+	    tests, tests == 1 ? "" : "s", errors,
+	    (tests - errors) * 100 / tests);
+    }
+
+    exit(errors);
+}
diff --git a/lib/iolog/regress/iolog_json/test1.in b/lib/iolog/regress/iolog_json/test1.in
new file mode 100644
index 000000000..8ad36894e
--- /dev/null
+++ b/lib/iolog/regress/iolog_json/test1.in
@@ -0,0 +1,34 @@
+{
+    "timestamp": {
+        "seconds": 1584993067,
+        "nanoseconds": 880288287
+    },
+    "columns": 80,
+    "command": "/usr/bin/make",
+    "lines": 24,
+    "runargv": [
+        "make",
+        "test"
+    ],
+    "runenv": [
+        "LANG=en_US.UTF-8",
+        "PATH=/bin:/sbin:/usr/games:/usr/bin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin",
+        "TERM=vt100",
+        "MAIL=/var/mail/root",
+        "LOGNAME=root",
+        "USER=root",
+        "HOME=/root",
+        "SHELL=/bin/ksh",
+        "SUDO_COMMAND=/usr/bin/make test",
+        "SUDO_USER=millert",
+        "SUDO_UID=8036",
+        "SUDO_GID=20",
+        "A__z=\"*SHLVL"
+    ],
+    "runuid": 0,
+    "runuser": "root",
+    "submitcwd": "/home/test",
+    "submithost": "sudo.ws",
+    "submituser": "millert",
+    "ttyname": "/dev/console"
+}
diff --git a/lib/iolog/regress/iolog_json/test2.in b/lib/iolog/regress/iolog_json/test2.in
new file mode 100644
index 000000000..df7170f1c
--- /dev/null
+++ b/lib/iolog/regress/iolog_json/test2.in
@@ -0,0 +1,28 @@
+{
+    "timestamp": { "seconds": 1584993067, "nanoseconds": 880288287 },
+    "columns": 80,
+    "command": "/usr/bin/make",
+    "lines": 24,
+    "runargv": [ "make", "test" ],
+    "runenv": [
+        "LANG=en_US.UTF-8",
+        "PATH=/bin:/sbin:/usr/games:/usr/bin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin",
+        "TERM=vt100",
+        "MAIL=/var/mail/root",
+        "LOGNAME=root",
+        "USER=root",
+        "HOME=/root",
+        "SHELL=/bin/ksh",
+        "SUDO_COMMAND=/usr/bin/make test",
+        "SUDO_USER=millert",
+        "SUDO_UID=8036",
+        "SUDO_GID=20",
+        "A__z=\"*SHLVL"
+    ],
+    "runuid": 0,
+    "runuser": "root",
+    "submitcwd": "/home/test",
+    "submithost": "sudo.ws",
+    "submituser": "millert",
+    "ttyname": "/dev/console"
+}
diff --git a/lib/iolog/regress/iolog_json/test2.out.ok b/lib/iolog/regress/iolog_json/test2.out.ok
new file mode 100644
index 000000000..8ad36894e
--- /dev/null
+++ b/lib/iolog/regress/iolog_json/test2.out.ok
@@ -0,0 +1,34 @@
+{
+    "timestamp": {
+        "seconds": 1584993067,
+        "nanoseconds": 880288287
+    },
+    "columns": 80,
+    "command": "/usr/bin/make",
+    "lines": 24,
+    "runargv": [
+        "make",
+        "test"
+    ],
+    "runenv": [
+        "LANG=en_US.UTF-8",
+        "PATH=/bin:/sbin:/usr/games:/usr/bin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin",
+        "TERM=vt100",
+        "MAIL=/var/mail/root",
+        "LOGNAME=root",
+        "USER=root",
+        "HOME=/root",
+        "SHELL=/bin/ksh",
+        "SUDO_COMMAND=/usr/bin/make test",
+        "SUDO_USER=millert",
+        "SUDO_UID=8036",
+        "SUDO_GID=20",
+        "A__z=\"*SHLVL"
+    ],
+    "runuid": 0,
+    "runuser": "root",
+    "submitcwd": "/home/test",
+    "submithost": "sudo.ws",
+    "submituser": "millert",
+    "ttyname": "/dev/console"
+}
diff --git a/lib/iolog/regress/iolog_json/test3.in b/lib/iolog/regress/iolog_json/test3.in
new file mode 100644
index 000000000..ea2df89b8
--- /dev/null
+++ b/lib/iolog/regress/iolog_json/test3.in
@@ -0,0 +1,22 @@
+{
+    "true": false,
+    "false": true,
+    "number": 1234567890,
+    "null": null,
+    "string": "nonsense",
+    "scope": {
+        "a": "b",
+        "bah": null
+    },
+    "array1": [
+        "foo",
+        "bar",
+        [
+            123,
+            null,
+            false,
+            "fizz",
+            "buzz"
+        ]
+    ]
+}
diff --git a/lib/util/json.c b/lib/util/json.c
index 1bc46572b..34deb828d 100644
--- a/lib/util/json.c
+++ b/lib/util/json.c
@@ -274,9 +274,14 @@ sudo_json_open_array_v1(struct json_container *json, const char *name)
 
     json_append_indent(json, json->indent_level);
 
-    json_append_string(json, name);
-    if (!json_append_buf(json, ": ["))
-	debug_return_bool(false);
+    if (name != NULL) {
+	json_append_string(json, name);
+	if (!json_append_buf(json, ": ["))
+	    debug_return_bool(false);
+    } else {
+	if (!json_append_buf(json, "["))
+	    debug_return_bool(false);
+    }
 
     json->indent_level += json->indent_increment;
     json->need_comma = false;
@@ -300,7 +305,7 @@ sudo_json_close_array_v1(struct json_container *json)
     debug_return_bool(true);
 }
 
-bool
+static bool
 sudo_json_add_value_int(struct json_container *json, const char *name,
     struct json_value *value, bool as_object)
 {