diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
index 8461c0e83e..54011c8f65 100644
--- a/Documentation/git-ls-files.txt
+++ b/Documentation/git-ls-files.txt
@@ -60,6 +60,11 @@ OPTIONS
 --stage::
 	Show staged contents' mode bits, object name and stage number in the output.
 
+--json::
+	Dump the entire index content in JSON format. This is for
+	debugging purposes and the JSON structure may change from time
+	to time.
+
 --directory::
 	If a whole directory is classified as "other", show just its
 	name (with a trailing slash) and not its whole contents.
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index 7f83c9a6f2..d00f6d3074 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -8,6 +8,7 @@
 #include "cache.h"
 #include "repository.h"
 #include "config.h"
+#include "json-writer.h"
 #include "quote.h"
 #include "dir.h"
 #include "builtin.h"
@@ -31,6 +32,7 @@ static int show_modified;
 static int show_killed;
 static int show_valid_bit;
 static int show_fsmonitor_bit;
+static int show_json;
 static int line_terminator = '\n';
 static int debug_mode;
 static int show_eol;
@@ -543,6 +545,8 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 			N_("show staged contents' object name in the output")),
 		OPT_BOOL('k', "killed", &show_killed,
 			N_("show files on the filesystem that need to be removed")),
+		OPT_BOOL(0, "json", &show_json,
+			N_("dump index content in json format")),
 		OPT_BIT(0, "directory", &dir.flags,
 			N_("show 'other' directories' names only"),
 			DIR_SHOW_OTHER_DIRECTORIES),
@@ -660,8 +664,12 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 
 	/* With no flags, we default to showing the cached files */
 	if (!(show_stage || show_deleted || show_others || show_unmerged ||
-	      show_killed || show_modified || show_resolve_undo))
+	      show_killed || show_modified || show_resolve_undo || show_json))
 		show_cached = 1;
+	if (show_json && (show_stage || show_deleted || show_others ||
+			  show_unmerged || show_killed || show_modified ||
+			  show_cached || show_resolve_undo || with_tree))
+		die(_("--show-json cannot be used with other --show- options, or --with-tree"));
 
 	if (with_tree) {
 		/*
@@ -673,10 +681,22 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		overlay_tree_on_index(the_repository->index, with_tree, max_prefix);
 	}
 
-	show_files(the_repository, &dir);
-
-	if (show_resolve_undo)
-		show_ru_info(the_repository->index);
+	if (!show_json) {
+		show_files(the_repository, &dir);
+
+		if (show_resolve_undo)
+			show_ru_info(the_repository->index);
+	} else {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		discard_index(the_repository->index);
+		the_repository->index->jw = &jw;
+		if (repo_read_index(the_repository) < 0)
+			die("index file corrupt");
+		puts(jw.json.buf);
+		the_repository->index->jw = NULL;
+		jw_release(&jw);
+	}
 
 	if (ps_matched) {
 		int bad;
diff --git a/cache.h b/cache.h
index bf20337ef4..84d0aeed20 100644
--- a/cache.h
+++ b/cache.h
@@ -326,6 +326,7 @@ static inline unsigned int canon_mode(unsigned int mode)
 #define UNTRACKED_CHANGED	(1 << 7)
 #define FSMONITOR_CHANGED	(1 << 8)
 
+struct json_writer;
 struct split_index;
 struct untracked_cache;
 
@@ -350,6 +351,7 @@ struct index_state {
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
 	struct mem_pool *ce_mem_pool;
+	struct json_writer *jw;
 };
 
 /* Name hashing */
diff --git a/json-writer.c b/json-writer.c
index aadb9dbddc..281bc50b39 100644
--- a/json-writer.c
+++ b/json-writer.c
@@ -202,6 +202,22 @@ void jw_object_null(struct json_writer *jw, const char *key)
 	strbuf_addstr(&jw->json, "null");
 }
 
+void jw_object_stat_data(struct json_writer *jw, const char *name,
+			 const struct stat_data *sd)
+{
+	jw_object_inline_begin_object(jw, name);
+	jw_object_intmax(jw, "st_ctime.sec", sd->sd_ctime.sec);
+	jw_object_intmax(jw, "st_ctime.nsec", sd->sd_ctime.nsec);
+	jw_object_intmax(jw, "st_mtime.sec", sd->sd_mtime.sec);
+	jw_object_intmax(jw, "st_mtime.nsec", sd->sd_mtime.nsec);
+	jw_object_intmax(jw, "st_dev", sd->sd_dev);
+	jw_object_intmax(jw, "st_ino", sd->sd_ino);
+	jw_object_intmax(jw, "st_uid", sd->sd_uid);
+	jw_object_intmax(jw, "st_gid", sd->sd_gid);
+	jw_object_intmax(jw, "st_size", sd->sd_size);
+	jw_end(jw);
+}
+
 static void increase_indent(struct strbuf *sb,
 			    const struct json_writer *jw,
 			    int indent)
diff --git a/json-writer.h b/json-writer.h
index 83906b09c1..38f9c9bf68 100644
--- a/json-writer.h
+++ b/json-writer.h
@@ -44,6 +44,8 @@
 
 #include "strbuf.h"
 
+struct stat_data;
+
 struct json_writer
 {
 	/*
@@ -81,6 +83,8 @@ void jw_object_true(struct json_writer *jw, const char *key);
 void jw_object_false(struct json_writer *jw, const char *key);
 void jw_object_bool(struct json_writer *jw, const char *key, int value);
 void jw_object_null(struct json_writer *jw, const char *key);
+void jw_object_stat_data(struct json_writer *jw, const char *key,
+			 const struct stat_data *sd);
 void jw_object_sub_jw(struct json_writer *jw, const char *key,
 		      const struct json_writer *value);
 
@@ -104,4 +108,21 @@ void jw_array_inline_begin_array(struct json_writer *jw);
 int jw_is_terminated(const struct json_writer *jw);
 void jw_end(struct json_writer *jw);
 
+/*
+ * These _gently versions accept NULL json_writer to reduce too much
+ * branching at the call site.
+ */
+static inline void jw_object_inline_begin_array_gently(struct json_writer *jw,
+						       const char *name)
+{
+	if (jw)
+		jw_object_inline_begin_array(jw, name);
+}
+
+static inline void jw_end_gently(struct json_writer *jw)
+{
+	if (jw)
+		jw_end(jw);
+}
+
 #endif /* JSON_WRITER_H */
diff --git a/read-cache.c b/read-cache.c
index 4dd22f4f6e..eec030b3bb 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -25,6 +25,7 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "json-writer.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -1952,6 +1953,50 @@ static void *load_index_extensions(void *_data)
 	return NULL;
 }
 
+static void dump_cache_entry(struct index_state *istate,
+			     int index,
+			     unsigned long offset,
+			     const struct cache_entry *ce)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct json_writer *jw = istate->jw;
+
+	jw_array_inline_begin_object(jw);
+
+	/*
+	 * this is technically redundant, but it's for easier
+	 * navigation when there hundreds of entries
+	 */
+	jw_object_intmax(jw, "id", index);
+
+	jw_object_string(jw, "name", ce->name);
+
+	strbuf_addf(&sb, "%06o", ce->ce_mode);
+	jw_object_string(jw, "mode", sb.buf);
+	strbuf_release(&sb);
+
+	jw_object_intmax(jw, "flags", ce->ce_flags);
+	/*
+	 * again redundant info, just so you don't have to decode
+	 * flags values manually
+	 */
+	if (ce->ce_flags & CE_VALID)
+		jw_object_true(jw, "assume-unchanged");
+	if (ce->ce_flags & CE_INTENT_TO_ADD)
+		jw_object_true(jw, "intent-to-add");
+	if (ce->ce_flags & CE_SKIP_WORKTREE)
+		jw_object_true(jw, "skip-worktree");
+	if (ce_stage(ce))
+		jw_object_intmax(jw, "stage", ce_stage(ce));
+
+	jw_object_string(jw, "oid", oid_to_hex(&ce->oid));
+
+	jw_object_stat_data(jw, "stat", &ce->ce_stat_data);
+	jw_object_intmax(jw, "file-offset", offset);
+
+	jw_end(jw);
+}
+
 /*
  * A helper function that will load the specified range of cache entries
  * from the memory mapped file and add them to the given index.
@@ -1972,6 +2017,9 @@ static unsigned long load_cache_entry_block(struct index_state *istate,
 		ce = create_from_disk(ce_mem_pool, istate->version, disk_ce, &consumed, previous_ce);
 		set_index_entry(istate, i, ce);
 
+		if (istate->jw)
+			dump_cache_entry(istate, i, src_offset, ce);
+
 		src_offset += consumed;
 		previous_ce = ce;
 	}
@@ -1983,6 +2031,8 @@ static unsigned long load_all_cache_entries(struct index_state *istate,
 {
 	unsigned long consumed;
 
+	jw_object_inline_begin_array_gently(istate->jw, "entries");
+
 	if (istate->version == 4) {
 		mem_pool_init(&istate->ce_mem_pool,
 				estimate_cache_size_from_compressed(istate->cache_nr));
@@ -1993,6 +2043,8 @@ static unsigned long load_all_cache_entries(struct index_state *istate,
 
 	consumed = load_cache_entry_block(istate, istate->ce_mem_pool,
 					0, istate->cache_nr, mmap, src_offset, NULL);
+
+	jw_end_gently(istate->jw);
 	return consumed;
 }
 
@@ -2120,6 +2172,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	size_t extension_offset = 0;
 	int nr_threads, cpus;
 	struct index_entry_offset_table *ieot = NULL;
+	int jw_pretty = 1;
 
 	if (istate->initialized)
 		return istate->cache_nr;
@@ -2154,6 +2207,8 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache_nr = ntohl(hdr->hdr_entries);
 	istate->cache_alloc = alloc_nr(istate->cache_nr);
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
+	istate->timestamp.sec = st.st_mtime;
+	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 	istate->initialized = 1;
 
 	p.istate = istate;
@@ -2176,6 +2231,20 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	if (!HAVE_THREADS)
 		nr_threads = 1;
 
+	if (istate->jw) {
+		jw_object_begin(istate->jw, jw_pretty);
+		jw_object_intmax(istate->jw, "version", istate->version);
+		jw_object_string(istate->jw, "oid", oid_to_hex(&istate->oid));
+		jw_object_intmax(istate->jw, "st_mtime.sec", istate->timestamp.sec);
+		jw_object_intmax(istate->jw, "st_mtime.nsec", istate->timestamp.nsec);
+
+		/*
+		 * Threading may mess up json writing. This is for
+		 * debugging only, so performance is not a concern.
+		 */
+		nr_threads = 1;
+	}
+
 	if (nr_threads > 1) {
 		extension_offset = read_eoie_extension(mmap, mmap_size);
 		if (extension_offset) {
@@ -2204,8 +2273,6 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		src_offset += load_all_cache_entries(istate, mmap, mmap_size, src_offset);
 	}
 
-	istate->timestamp.sec = st.st_mtime;
-	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 
 	/* if we created a thread, join it otherwise load the extensions on the primary thread */
 	if (extension_offset) {
@@ -2216,6 +2283,8 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		p.src_offset = src_offset;
 		load_index_extensions(&p);
 	}
+	jw_end_gently(istate->jw);
+
 	munmap((void *)mmap, mmap_size);
 
 	/*
