Called the "Diary of a mortar round in Damascus", the page provides information on how many were launched, where they struck and the number of casualties.
The data helps residents avoid areas that come under fire from rebels entrenched in suburbs around the capital, which has been spared the worst of the more than three-year-old conflict.
"Each mortar is a story in itself, a suffering," said Anas Aswad, one of five youth administrators who set up the Facebook page, which is followed by more than 300,000 people.
"At the end of the day, our martyrs are not only numbers," said Aswad.
Syria's conflict is estimated to have killed more than 180,000 people and displaced around half of the population since it broke out in March 2011.
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After a series of stunning rebel advances around Damascus in 2012, the army has slowly reclaimed a string of hotspots in the past two years.
But rebels seeking to make the regime ease its attacks on areas they hold near the capital continue to fire mortar rounds and rockets at Damascus each day.
Rana, 36, said she consults the page regularly to map out her travel in Damascus and changes her itinerary to avoid areas where mortars have fallen.
"It is an intelligent and useful initiative," she said.
According to the Facebook page, a record 150 mortar rounds fell on different sectors of Damascus on June 3, the day Assad secured a new term in a controversial election.