$comment (Query Comment)
Last updated: 2026-10-09
$comment (Query Comment)
$comment attaches explanatory text to a query so you can trace its origin in currentOp, the slow-query log and the profiler. `{ $comment: 'checkout-cart-query' }` or chained as db.coll.find(...).comment('checkout'). It does not affect results or index selection. Use it to tag queries for ops diagnostics.
| Category | Projection |
|---|---|
| MongoDB Version | 4.4+ |
| Example Language | mongosh (Shell) |
📝 Syntax
{ $comment: <comment string> }⚙️ Parameters
| comment string | Arbitrary text that appears in diagnostics. |
|---|
Returns：Query results (unaffected by the comment)
▶ Example
Run the commands below in your local mongosh (requires a running mongod):
// $comment: tag the query for ops
db.orders.find(
{ status: 'pending' },
{ _id: 1 }
).comment('checkout-pending-orders')Output：
// Results are unchanged; the comment is recorded in diagnostics📌 Notes
- Does not change results or the execution plan
- Visible in slow-query logs, currentOp and profile
- Aggregation pipelines accept a comment option too
🏷️ Related Tags
💡 Related Cases
More hands-on cases coming soon.
📚 Related Tutorials
❓ FAQ
QDoes $comment change query results?
ANo, it is metadata only and does not affect results or index selection.
QWhere can I see the comment?
AIn currentOp and the slow-query log (system.profile).
QCan aggregation queries carry comments?
AYes, db.coll.aggregate([...], { comment: '...' }).
