You can use the application here.
This utility runs client-side. No data is sent to any servers, including the Blockchain.
The bulk of the utility is found in the application's index file.
If you would like the word list for your own use you can find that here.
You can test the application using the following data:
TGuhK7nePWEYdkvScq5eXVnZLZAGPA8Taf
1. ecology
2. traffic
3. hold
4. off
5. fossil
6.
7. canal
8. skill
9. exile
10. jealous
11. option
12. agent
13. health
14. hat
15. process
16. winter
17. desk
18. glimpse
19. spirit
20. baby
21. odor
22. deposit
23. hill
24. history
Enter the address, set the missing word to be the 6th and enter the rest of the words. The utility will yield the missing word adult.