diff --git a/src/package.lisp b/src/package.lisp
index 76c6a0b..a598b8d 100644
--- a/src/package.lisp
+++ b/src/package.lisp
@@ -416,11 +416,12 @@
    :html->text))
 
 (defpackage :resources-utils
-  (:use :cl
+  (:use
+   :cl
    :cl-ppcre
-        :config
+   :config
    :constants
-        :filesystem-utils
+   :filesystem-utils
    :text-utils)
   (:nicknames :res)
   (:export
@@ -434,6 +435,18 @@
    :get-sys-config-file
    :get-data-file))
 
+(defpackage :zip-info
+  (:use
+   :cl
+   :cl-ppcre
+   :config
+   :constants
+   :filesystem-utils
+   :text-utils
+   :misc-utils)
+  (:export
+   :zip-file-p))
+
 (defpackage :crypto-utils
   (:use :cl
    :alexandria
diff --git a/src/zip-info.lisp b/src/zip-info.lisp
new file mode 100644
index 0000000..f7531d7
--- /dev/null
+++ b/src/zip-info.lisp
@@ -0,0 +1,88 @@
+;; tinmop: an humble gemini and pleroma client
+;; Copyright (C) 2021  cage
+
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+(in-package :zip-info)
+
+(alexandria:define-constant +byte-type+                '(unsigned-byte 8) :test #'equalp)
+
+(alexandria:define-constant +eocd-signature+                   #x06054b50 :test #'=)
+
+(alexandria:define-constant +eocd-signature-size+                       4 :test #'=)
+
+(alexandria:define-constant +eocd-number-of-disk+                       2 :test #'=)
+
+(alexandria:define-constant +eocd-number-of-disk-w/start-eocd+          2 :test #'=)
+
+(alexandria:define-constant +eocd-tot-no-entry-cd-this-disk+            2 :test #'=)
+
+(alexandria:define-constant +eocd-tot-no-entry-cd+                      2 :test #'=)
+
+(alexandria:define-constant +eocd-cd-size+                              4 :test #'=)
+
+(alexandria:define-constant +eocd-cd-offset+                            4 :test #'=)
+
+(alexandria:define-constant +eocd-zip-file-comment-length+              2 :test #'=)
+
+(alexandria:define-constant +eocd-fixed-size+   (+ +eocd-signature-size+
+                                                   +eocd-number-of-disk+
+                                                   +eocd-number-of-disk-w/start-eocd+
+                                                   +eocd-tot-no-entry-cd-this-disk+
+                                                   +eocd-tot-no-entry-cd+
+                                                   +eocd-cd-size+
+                                                   +eocd-cd-offset+
+                                                   +zip-file-comment-length+)
+  :test #'=)
+
+(alexandria:define-constant +eocd-zip-file-comment-offset+ (- +eocd-fixed-size+
+                                                              +zip-file-comment-length+)
+  :test #'=)
+
+(defun open-file (path)
+  (open path :element-type +byte-type+ :direction :input :if-does-not-exist :error))
+
+(defun close-file (stream)
+  (close stream))
+
+(defmacro with-open-zip-file ((stream path) &body body)
+  `(let ((,stream (open-file ,path)))
+     (unwind-protect
+        (progn ,@body)
+       (close-file ,stream))))
+
+(defun read-bytes->int (stream size)
+  (misc:byte->int (loop repeat size collect (read-byte stream))))
+
+(defun zip-file-p (path)
+  (let ((file-size  (file-size path))
+        (eocd-start nil))
+    (when (>= file-size +eocd-fixed-size+)
+      (with-open-zip-file (stream path)
+        (loop named signature-finder for position
+              from (- file-size +eocd-signature-size+)
+              downto 0 do
+          (file-position stream position)
+          (let ((maybe-signature (read-bytes->int stream +eocd-signature-size+)))
+            (when (= maybe-signature +eocd-signature+)
+              (setf eocd-start position)
+              (return-from signature-finder t))))
+        (when eocd-start
+          (let* ((eocd-fixed-part-offset         (+ eocd-start +eocd-fixed-size+))
+                 (eocd-offset-minus-zip-comment  (- eocd-fixed-part-offset
+                                                    +eocd-zip-file-comment-length+)))
+            (file-position stream eocd-offset-minus-zip-comment)
+            (let ((comment-size (read-bytes->int stream +zip-file-comment-length+)))
+              (= (+ eocd-fixed-part-offset comment-size)
+                 file-size))))))))
diff --git a/tinmop.asd b/tinmop.asd
index e05df77..44ebf8f 100644
--- a/tinmop.asd
+++ b/tinmop.asd
@@ -67,6 +67,7 @@
                (:file "html-utils")
                (:file "crypto-utils")
                (:file "resources-utils")
+               (:file "zip-info")
                (:file "interfaces")
                (:file "mtree-utils")
                (:file "bs-tree")