nips/22.md

NIP-22
======

Event `created_at` Limits
---------------------------

`draft` `optional` `author:jeffthibault` `author:Giszmo`

Relays may define both upper and lower limits within which they will consider an event's `created_at` to be acceptable. Both the upper and lower limits MUST be unix timestamps in seconds as defined in [NIP-01](01.md).

If a relay supports this NIP, the relay SHOULD send the client a `NOTICE` message saying the event was not stored for the `created_at` timestamp not being within the permitted limits.

Client Behavior
---------------

Clients SHOULD use the [NIP-11](11.md) `supported_nips` field to learn if a relay uses event `created_at` time limits as defined by this NIP.

Motivation
----------

This NIP formalizes restrictions on event timestamps as accepted by a relay and allows clients to be aware of relays that have these restrictions.

The event `created_at` field is just a unix timestamp and can be set to a time in the past or future. Relays accept and share events dated to 20 years ago or 50,000 years in the future. This NIP aims to define a way for relays that do not want to store events with *any* timestamp to set their own restrictions.

[Replaceable events](16.md#replaceable-events) can behave rather unexpected if the user wrote them - or tried to write them - with a wrong system clock. Persisting an update with a backdated system now would result in the update not getting persisted without a `NOTICE` and if they did the last update with a forward dated system, they will again fail to do another update with the now correct time.

A wide adoption of this nip could create a better user experience as it would decrease the amount of events that appear wildly out of order or even from impossible dates in the distant past or future.

Python Example
--------------

```python
import time

TIME = int(time.now)
LOWER_LIMIT = TIME - (60 * 60 * 24) # Define lower limit as 1 day into the past
UPPER_LIMIT = TIME + (60 * 15)      # Define upper limit as 15 minutes into the future

if event.created_at not in range(LOWER_LIMIT, UPPER_LIMIT):
  # NOTE: This is one example of a notice message. Relays can change this to notify clients however they like.
  ws.send('["NOTICE", "The event created_at field is out of the acceptable range (-24h, +15min) for this relay and was not stored."]')
```