MongoDB ObjectId Converter

Every default MongoDB _id already records when the document was created, so you can often answer "when did this arrive?" without a createdAt field. Paste ObjectIds in any common form: 24 hex digits, ObjectId("..."), the extended JSON { "$oid": "..." } from an export, or 16 Base64 characters from a driver or log. The tool splits the 12 bytes into the 4-byte timestamp, the 5-byte random value and the 3-byte counter, shows the time in UTC, as a Unix timestamp and in your time zone, and summarizes how many processes a batch of IDs came from. It also works in reverse. Enter a date or Unix timestamp and you get the lowest and highest ObjectId possible in that second, plus a mongosh find() with $gte and $lt on _id, which lets you pull a time range using the _id index. Past January 2038 the top bit of the timestamp is set, and drivers and the server disagree on the date: mongosh reads it as unsigned, while $toDate on the server reads it as signed and returns a date between 1901 and 1969. The tool shows both. Decoding was compared with getTimestamp() and $toDate on MongoDB 7.0.43 for 3,004 ObjectIds, and date conversion with ObjectId.createFromTime(). Everything runs in your browser, so no IDs are uploaded.