diff --git a/tools/cmd/diff/collect.go b/tools/cmd/diff/collect.go
index c18417384..787d35168 100644
--- a/tools/cmd/diff/collect.go
+++ b/tools/cmd/diff/collect.go
@@ -4,13 +4,64 @@ package diff
 
 import (
 	"fmt"
+	"kitty/tools/utils"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 var _ = fmt.Print
 var path_name_map, remote_dirs map[string]string
 
+var mimetypes_cache, data_cache *utils.LRUCache[string, string]
+var lines_cache *utils.LRUCache[string, []string]
+
+func init_caches() {
+	mimetypes_cache = utils.NewLRUCache[string, string](4096)
+	data_cache = utils.NewLRUCache[string, string](4096)
+	lines_cache = utils.NewLRUCache[string, []string](4096)
+}
+
+func mimetype_for_path(path string) string {
+	return mimetypes_cache.MustGetOrCreate(path, func(path string) string {
+		mt := utils.GuessMimeTypeWithFileSystemAccess(path)
+		if mt == "" {
+			mt = "application/octet-stream"
+		}
+		if utils.KnownTextualMimes[mt] {
+			if _, a, found := strings.Cut(mt, "/"); found {
+				mt = "text/" + a
+			}
+		}
+		return mt
+	})
+}
+
+func data_for_path(path string) (string, error) {
+	return data_cache.GetOrCreate(path, func(path string) (string, error) {
+		ans, err := os.ReadFile(path)
+		return utils.UnsafeBytesToString(ans), err
+	})
+}
+
+func sanitize(x string) string {
+	x = strings.ReplaceAll(x, "\r\n", "⏎\n")
+	return utils.SanitizeControlCodes(x, "░")
+}
+
+func lines_for_path(path string) ([]string, error) {
+	return lines_cache.GetOrCreate(path, func(path string) ([]string, error) {
+		ans, err := data_for_path(path)
+		if err != nil {
+			return nil, err
+		}
+		ans = sanitize(strings.ReplaceAll(ans, "\t", conf.Replace_tab_by))
+		lines := make([]string, 0, 256)
+		splitlines_like_git(ans, false, func(line string) { lines = append(lines, line) })
+		return lines, nil
+	})
+}
+
 type Collection struct {
 }
 
diff --git a/tools/cmd/diff/main.go b/tools/cmd/diff/main.go
index eda62d2af..48eb0d6b9 100644
--- a/tools/cmd/diff/main.go
+++ b/tools/cmd/diff/main.go
@@ -51,6 +51,7 @@ func main(_ *cli.Command, opts_ *Options, args []string) (rc int, err error) {
 	if err = set_diff_command(conf.Diff_cmd); err != nil {
 		return 1, err
 	}
+	init_caches()
 	left, right := get_remote_file(args[0]), get_remote_file(args[1])
 	if isdir(left) != isdir(right) {
 		return 1, fmt.Errorf("The items to be diffed should both be either directories or files. Comparing a directory to a file is not valid.'")
diff --git a/tools/cmd/diff/patch.go b/tools/cmd/diff/patch.go
index d4dc8345c..055f1a4f7 100644
--- a/tools/cmd/diff/patch.go
+++ b/tools/cmd/diff/patch.go
@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"kitty/tools/utils"
+	"kitty/tools/utils/images"
 	"kitty/tools/utils/shlex"
 	"os/exec"
 	"path/filepath"
@@ -52,6 +53,223 @@ func set_diff_command(q string) error {
 	return err
 }
 
+type Chunk struct {
+	is_context              bool
+	left_start, right_start int
+	left_count, right_count int
+	centers                 []struct{ prefix_count, suffix_count int }
+}
+
+func (self *Chunk) add_line() {
+	self.right_count++
+}
+
+func (self *Chunk) remove_line() {
+	self.left_count++
+}
+
+func (self *Chunk) context_line() {
+	self.left_count++
+	self.right_count++
+}
+
+func changed_center(left, right string) (ans struct{ prefix_count, suffix_count int }) {
+	if len(left) > 0 && len(right) > 0 {
+		ll, rl := len(left), len(right)
+		ml := utils.Min(ll, rl)
+		for ans.prefix_count < ml && left[ans.prefix_count] == right[ans.prefix_count] {
+			ans.prefix_count++
+		}
+		if ans.prefix_count < ml {
+			for ans.suffix_count < ml-ans.prefix_count && left[ll-1-ans.suffix_count] == right[rl-1-ans.suffix_count] {
+				ans.suffix_count++
+			}
+		}
+	}
+	return
+}
+
+func (self *Chunk) finalize(left_lines, right_lines []string) {
+	if !self.is_context && self.left_count == self.right_count {
+		for i := 0; i < self.left_count; i++ {
+			self.centers = append(self.centers, changed_center(left_lines[self.left_start+i], right_lines[self.right_start+i]))
+		}
+	}
+}
+
+type Hunk struct {
+	left_start, left_count     int
+	right_start, right_count   int
+	title                      string
+	added_count, removed_count int
+	chunks                     []*Chunk
+	current_chunk              *Chunk
+	largest_line_number        int
+}
+
+func (self *Hunk) new_chunk(is_context bool) *Chunk {
+	left_start, right_start := self.left_start, self.right_start
+	if len(self.chunks) > 0 {
+		c := self.chunks[len(self.chunks)-1]
+		left_start = c.left_start + c.left_count
+		right_start = c.right_start + c.right_count
+	}
+	return &Chunk{is_context: is_context, left_start: left_start, right_start: right_start}
+}
+
+func (self *Hunk) ensure_diff_chunk() {
+	if self.current_chunk == nil || self.current_chunk.is_context {
+		if self.current_chunk != nil {
+			self.chunks = append(self.chunks, self.current_chunk)
+		}
+		self.current_chunk = self.new_chunk(false)
+	}
+}
+
+func (self *Hunk) ensure_context_chunk() {
+	if self.current_chunk == nil || !self.current_chunk.is_context {
+		if self.current_chunk != nil {
+			self.chunks = append(self.chunks, self.current_chunk)
+		}
+		self.current_chunk = self.new_chunk(true)
+	}
+}
+
+func (self *Hunk) add_line() {
+	self.ensure_diff_chunk()
+	self.current_chunk.add_line()
+	self.added_count++
+}
+
+func (self *Hunk) remove_line() {
+	self.ensure_diff_chunk()
+	self.current_chunk.remove_line()
+	self.removed_count++
+}
+
+func (self *Hunk) context_line() {
+	self.ensure_context_chunk()
+	self.current_chunk.context_line()
+}
+
+func (self *Hunk) finalize(left_lines, right_lines []string) error {
+	if self.current_chunk != nil {
+		self.chunks = append(self.chunks, self.current_chunk)
+	}
+	// Sanity check
+	c := self.chunks[len(self.chunks)-1]
+	if c.left_start+c.left_count != self.left_start+self.left_count {
+		return fmt.Errorf("Left side line mismatch %d != %d", c.left_start+c.left_count, self.left_start+self.left_count)
+	}
+	if c.right_start+c.right_count != self.right_start+self.right_count {
+		return fmt.Errorf("Right side line mismatch %d != %d", c.right_start+c.right_count, self.right_start+self.right_count)
+	}
+	for _, c := range self.chunks {
+		c.finalize(left_lines, right_lines)
+	}
+	return nil
+}
+
+type Patch struct {
+	all_hunks                                       []*Hunk
+	largest_line_number, added_count, removed_count int
+}
+
+func (self *Patch) Len() int { return len(self.all_hunks) }
+
+func splitlines_like_git(raw string, strip_trailing_lines bool, process_line func(string)) {
+	sz := len(raw)
+	if strip_trailing_lines {
+		for sz > 0 && (raw[sz-1] == '\n' || raw[sz-1] == '\r') {
+			sz--
+		}
+	}
+	start := 0
+	for i := 0; i < sz; i++ {
+		switch raw[i] {
+		case '\n':
+			process_line(raw[start:i])
+			start = i + 1
+		case '\r':
+			process_line(raw[start:i])
+			start = i + 1
+			if start < sz && raw[start] == '\n' {
+				i++
+				start++
+			}
+		}
+	}
+	if start < sz {
+		process_line(raw[start:sz])
+	}
+}
+
+func parse_range(x string) (start, count int) {
+	s, c, found := strings.Cut(x, ",")
+	start, _ = strconv.Atoi(s)
+	if start < 0 {
+		start = -start
+	}
+	count = 1
+	if found {
+		count, _ = strconv.Atoi(c)
+	}
+	return
+}
+
+func parse_hunk_header(line string) *Hunk {
+	parts := strings.SplitN(line, "@@", 3)
+	linespec := strings.TrimSpace(parts[1])
+	title := ""
+	if len(parts) == 3 {
+		title = strings.TrimSpace(parts[2])
+	}
+	left, right, _ := strings.Cut(linespec, " ")
+	ls, lc := parse_range(left)
+	rs, rc := parse_range(right)
+	return &Hunk{
+		title: title, left_start: ls - 1, left_count: lc, right_start: rs - 1, right_count: rc,
+		largest_line_number: utils.Max(ls-1+lc, rs-1+rc),
+	}
+}
+
+func parse_patch(raw string, left_lines, right_lines []string) (ans *Patch, err error) {
+	ans = &Patch{all_hunks: make([]*Hunk, 0, 32)}
+	var current_hunk *Hunk
+	splitlines_like_git(raw, true, func(line string) {
+		if strings.HasPrefix(line, "@@ ") {
+			current_hunk = parse_hunk_header(line)
+			ans.all_hunks = append(ans.all_hunks, current_hunk)
+		} else if current_hunk != nil {
+			var ch byte
+			if len(line) > 0 {
+				ch = line[0]
+			}
+			switch ch {
+			case '+':
+				current_hunk.add_line()
+			case '-':
+				current_hunk.remove_line()
+			case '\\':
+			default:
+				current_hunk.context_line()
+			}
+		}
+	})
+	for _, h := range ans.all_hunks {
+		err = h.finalize(left_lines, right_lines)
+		if err != nil {
+			return
+		}
+		ans.added_count += h.added_count
+		ans.removed_count += h.removed_count
+	}
+	if len(ans.all_hunks) > 0 {
+		ans.largest_line_number = ans.all_hunks[len(ans.all_hunks)-1].largest_line_number
+	}
+	return
+}
+
 func run_diff(file1, file2 string, num_of_context_lines int) (ok, is_different bool, patch string, err error) {
 	context := strconv.Itoa(num_of_context_lines)
 	cmd := utils.Map(func(x string) string {
@@ -82,3 +300,50 @@ func run_diff(file1, file2 string, num_of_context_lines int) (ok, is_different b
 	}
 	return true, false, stdout.String(), nil
 }
+
+func do_diff(file1, file2 string, context_count int) (ans *Patch, err error) {
+	ok, _, raw, err := run_diff(file1, file2, context_count)
+	if !ok {
+		return nil, fmt.Errorf("Failed to diff %s vs. %s with errors:\n%s", file1, file2, raw)
+	}
+	if err != nil {
+		return
+	}
+	left_lines, err := lines_for_path(file1)
+	if err != nil {
+		return
+	}
+	right_lines, err := lines_for_path(file2)
+	if err != nil {
+		return
+	}
+	ans, err = parse_patch(raw, left_lines, right_lines)
+	return
+}
+
+func diff(jobs []struct{ file1, file2 string }, context_count int) (ans map[string]*Patch, err error) {
+	ans = make(map[string]*Patch)
+	ctx := images.Context{}
+	type result struct {
+		file1, file2 string
+		err          error
+		patch        *Patch
+	}
+	results := make(chan result)
+	ctx.Parallel(0, len(jobs), func(nums <-chan int) {
+		for i := range nums {
+			job := jobs[i]
+			r := result{file1: job.file1, file2: job.file2}
+			r.patch, r.err = do_diff(job.file1, job.file2, context_count)
+			results <- r
+		}
+	})
+	close(results)
+	for r := range results {
+		if r.err != nil {
+			return nil, r.err
+		}
+		ans[r.file1] = r.patch
+	}
+	return ans, nil
+}
diff --git a/tools/utils/misc.go b/tools/utils/misc.go
index 5e54fd5de..f6e63b607 100644
--- a/tools/utils/misc.go
+++ b/tools/utils/misc.go
@@ -4,6 +4,7 @@ package utils
 
 import (
 	"fmt"
+	"regexp"
 	"sort"
 
 	"golang.org/x/exp/constraints"
@@ -143,3 +144,15 @@ func Memset[T any](dest []T, pattern ...T) []T {
 	}
 	return dest
 }
+
+var ControlCodesPat = (&Once[*regexp.Regexp]{Run: func() *regexp.Regexp {
+	return regexp.MustCompile("[\x00-\x09\x0b-\x1f\x7f\x80-\x9f]")
+}}).Get
+
+func SanitizeControlCodes(raw string, replace_with ...string) string {
+	r := ""
+	if len(replace_with) > 0 {
+		r = replace_with[0]
+	}
+	return ControlCodesPat().ReplaceAllLiteralString(raw, r)
+}