diff --git a/docs/tools.md b/docs/tools.md
index 5a7298d34f8b4e7aadb067e8fbc43f73b8d0f14f..eb731a5268ebd75bed6cdb93165f9d3b4760623f 100644
--- a/docs/tools.md
+++ b/docs/tools.md
@@ -2,6 +2,8 @@
 layout: default
 ---
 
+[(back)](./)
+
 # Available Tools
 
 | Tool | Authors | Notes |
@@ -59,3 +61,5 @@ layout: default
 | [Pairwise Pict Online](https://pairwise.yuuniworks.com/) | [Tamura] | PICT on the web | 
 | [CoverTable](https://github.com/walkframe/covertable) | [Yasuyuki] | Python and TypeScript. Open source | 
 
+# Links
+* [Comparison of efficiency](./efficiency.md)