doc: write overview on slab tab in tcm ui

Author: maryiaLichko

doc/tooling/tcm/_images/tcm_ui_slabs.png

@@ -36,7 +36,7 @@ To log into |tcm| after bootstrap, use the following credentials:
 After logging in with the default password:
 
 #.  Adjust the :ref:`password policy <tcm_access_control_password_policy>`
-    in accordance to the security requirements that apply in your organization.
+    in accordance with the security requirements that apply in your organization.
 #.  Change the ``admin`` user's password on the :ref:`User settings <tcm_ui_user_settings>` page.
 
 To log out of |tcm|, click the user's name in the header and click **Log out**.
@@ -64,7 +64,7 @@ Onboarding
 ----------
 
 The **Onboarding** item of the navigation pane starts the interactive onboarding
-tutorial. Use it to get familiar with main |tcm| features directly in the web interface.
+tutorial. Use it to get familiar with the main |tcm| features directly in the web interface.
 
 ..  _tcm_ui_visibility:
 
@@ -92,7 +92,7 @@ There are the following page groups:
 -   **Tools**: |tcm| administration.
 -   **Settings**: runtime management of |tcm| settings.
 
-Read on to learn what you can do on pages of these groups.
+Read on to learn what you can do on the pages of these groups.
 
 ..  _tcm_ui_cluster:
 
@@ -156,14 +156,72 @@ The instance page has an **Actions** menu at the top that allows you to:
 -   edit the instance configuration
 -   remove the instance
 
+Slabs tab overview
+^^^^^^^^^^^^^^^^^^
+
+The **Slabs** tab in the TCM Web UI visualizes memory allocation within each Tarantool instance using the slab allocator.
+
+This tab is useful for:
+
+- Identifying memory fragmentation
+- Analyzing cache saturation by object size
+- Debugging excessive memory use in real time
+
+
+This visualization is based on the output of:
+
+.. code-block:: lua
+
+    box.slab.stats()
+
+This function returns a Lua table with per-class (per object size) memory allocation statistics from the slab allocator.
+
+Each entry in the output contains:
+
+- ``item_size``: object size class
+- ``slab_count``: number of slab blocks
+- ``slab_size``: memory size of each slab
+- ``item_count``: number of allocated objects
+- ``mem_used``: bytes used
+- ``mem_free``: bytes free
+
+These values are parsed and rendered as visual elements in the UI.
+
+Each block represents a single slab (a fixed-size memory region). The color indicates how full the slab is:
+
+- **Green** — slab is partially filled
+- **Red** — slab is full (100% usage)
+
+.. image:: _images/tcm_ui_slabs.png
+   :width: 700px
+
+
+
+If multiple slabs are shown for the same object size, each slab’s fill level is calculated individually and visualized accordingly.
+Each row represents a cache class (object allocation group) for a specific `item_size`.
+
+The overall fill percentage for a cache class is calculated using:
+
+.. code-block:: text
+
+    fill % = (item_count * item_size) / (slab_count * slab_size)
+
+However, each slab is visualized individually, so different fill levels across slabs will result in various colors within the same row.
+
+Slab allocation may vary between Tarantool instances within the same replica set due to:
+
+- Runs in a separate process
+- Allocates memory independently
+- May receive different workloads or query patterns
+
 ..  _tcm_ui_cluster_config:
 
 Configuration
 ~~~~~~~~~~~~~
 
 The cluster **Configuration** page provides an interactive editor for the cluster
 :ref:`configuration <configuration>`. It is connected to the centralized configuration
-storage that the cluster uses. All changes you make and apply on this page are
+storage that the cluster uses. All changes you make and apply to this page are
 sent to this centralized storage.
 
 .. image:: _images/tcm_ui_config.png
@@ -211,7 +269,7 @@ Tuples
     The cluster-wide access to stored data on the **Tuples** page is supported only
     for sharded clusters that use the `CRUD <https://github.com/tarantool/crud>`__ module.
 
-The **Tuples** page provides access to data stored in user spaces of the selected
+The **Tuples** page provides access to data stored in the user spaces of the selected
 cluster.
 
 .. image:: _images/tcm_ui_tuples.png
@@ -221,7 +279,7 @@ cluster.
 
 On this page, you can:
 
--   view the list of user spaces, their size and engines
+-   view the list of user spaces, their size, and engines
 -   view and edit tuples stored in user spaces
 
 ..  _tcm_ui_cluster_tcf:
@@ -273,7 +331,7 @@ including system spaces.
 
 On this page, you can:
 
--   view and edit instance spaces, their size and engines
+-   view and edit instance spaces, their size, and engines
 -   view and edit tuples stored in all spaces of the instance
 
 ..  _tcm_ui_clusters: