How do I get the creation date from a MongoDB ObjectId?

The first 4 bytes (first 8 hex characters) are a Unix timestamp in seconds. Convert that hex to a number and read it as seconds since the epoch. This tool does it for you.

Are ObjectIds sequential or sortable?

Roughly. The leading timestamp makes them sortable by creation time to the second, and the counter keeps ids created within the same second ordered, but they are not strictly sequential across processes.

Is an ObjectId globally unique?

In practice yes. The timestamp, per-process random value, and incrementing counter make collisions extremely unlikely, even across many machines.

MongoDB ObjectId Decoder

Paste a MongoDB ObjectId to reveal the creation timestamp, random value, and counter packed inside it. You can also build an ObjectId for any date, handy for _id range queries. Nothing leaves your browser.

More information about MongoDB ObjectIds

Every MongoDB document has an _id, and by default it's an ObjectId: a 12-byte value shown as 24 hexadecimal characters. It isn't random, it's structured, which is why you can pull a creation time straight out of it.

What's inside an ObjectId?

4 bytes, timestamp: seconds since the Unix epoch, when the ObjectId was created.
5 bytes, random value: unique per process (in the legacy pre-3.4 format this was a 3-byte machine id plus a 2-byte process id).
3 bytes, counter: an incrementing value, so ids created in the same second stay unique and roughly ordered.

Why it's useful

Because the timestamp is the first 4 bytes, ObjectIds are roughly sortable by creation time, and you can query by time range without a separate date field: { _id: { $gt: ObjectId("...") } }. Use the "ObjectId for a date" box above to build the boundary value.

Frequently asked questions

VisuaLeaf

Browse and query ObjectIds visually in VisuaLeaf

VisuaLeaf shows human-readable timestamps for your ObjectIds, lets you build _id range queries visually, and gives you a full MongoDB and SQL client with query builders, schema diagrams, and charts.

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