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The Reminders feature turns channel topics into cron schedules. When the bot starts (or a channel is created or updated), it reads the topic, parses any reminder definitions, and schedules recurring messages with threads.

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Topic format

Embed one or more reminders in a channel’s topic using the following syntax: 
[reminder:CRON_EXPRESSION:MESSAGE]
You can include multiple reminders in the same topic: 
Weekly standup channel. [reminder:0 9 * * 1:Weekly standup time!] [reminder:0 17 * * 5:Week in review!]
Standard 5-field cron expressions are supported (minute, hour, day-of-month, month, day-of-week). Effect’s Cron module parses the expression — invalid expressions are logged and skipped.

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What happens on schedule

When a cron fires, the bot:
  1. Posts the reminder message to the channel.
  2. Creates a thread from that message named {date} - {message} (e.g. Mon Mar 25 2026 - Weekly standup time!).
If the thread creation fails, it retries up to 3 times with a 1-second delay between attempts.
Reminders.ts
const createThreadPolicy = Schedule.spaced("1 seconds").pipe(
  Schedule.both(Schedule.recurs(3)),
)

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Parsing the topic

The parseTopic function uses a regular expression to extract all [reminder:...:...] blocks and parses each cron expression independently:
Reminders.ts
const parseTopic = (topic: string) =>
  Effect.partition(
    Array.from(topic.matchAll(/\[reminder:(.+?):(.+?)\]/g)),
    (matches) => {
      const [match, expression, message] = matches
      if (
        match === undefined ||
        expression === undefined ||
        message === undefined
      ) {
        return Effect.fail(
          new InvalidTopic({
            reason: "invalid reminder format",
            match: String(match),
          }),
        )
      }
      return parseExpression(match, expression, message)
    },
  )
Invalid entries are logged as info-level messages and do not prevent valid reminders in the same topic from being scheduled.

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Gateway events

The bot listens to the following Discord gateway events to keep schedules in sync:
EventAction
GUILD_CREATESchedules reminders for all channels in the guild on startup.
CHANNEL_CREATESchedules reminders for the new channel.
CHANNEL_UPDATECancels existing schedules and re-parses the updated topic.
CHANNEL_DELETECancels any running schedules for the deleted channel.

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Example

To post a weekly standup reminder every Monday at 9:00 AM UTC, set the channel topic to: 
[reminder:0 9 * * 1:Weekly standup time!]
At 9:00 AM every Monday the bot posts “Weekly standup time!” and opens a thread for discussion.

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