If someone changes the description of a card, it may appear that the entire description has been deleted. However, Trello tracks these changes in the background so you can recover the original description later. Although the old description isn't currently visible via the Trello web interface, the data is available via the API and it's relatively easy to locate.
Instructions for recovering a description
Get the card ID for the card. This is included in the URL of the card, after the /c/—e.g. hpAcP7IS is the card ID for https://trello.com/c/hpAcP7IS/814-multiple-log-in-credentials
Log into Trello in Chrome or Firefox.
Go to https://trello.com/1/cards/[card ID]/actions?filter=updateCard:desc, replacing [card ID] with the card ID you noted above.
Look for data.old.desc for the old descriptions
Instructions for recovering a card title
Export the card in question to a JSON file via the Share menu of the card.
Look for the actions section of the JSON and where the previous card name will be recorded.
Additional Technical Explanation
For example, let's say we want to view the old descriptions of one of the cards on the development board, https://trello.com/c/hpAcP7IS/814-multiple-log-in-credentials. The description has changed several times and we want to see what is used to be. Take note of the card's ID in the URL, which is hpAcP7IS.
The API route we want to use is GET /1/cards/[card id or shortlink]/actions, adding ?filter=updateCard:desc to the end so we only see changes to the description. Because this is a GET route, all you need to do is log into Trello in your browser and put the URL in the address bar.
Using that API route with the example card above, hpAcP7IS, our URL will be: https://trello.com/1/cards/hpAcP7IS/actions?filter=updateCard:desc. Within the results, you'll see actions for each time the description was changed, where you'll see data.card.desc (the new description) and data.old.desc (the old description).
More Guidance on Working with JSON
For more information on how to manipulate JSON data, please check out Making Sense of Trello's JSON Export.
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