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Email & Inbox

Email Thread Summarizer

Long threads collapse into a summary with the decision and the action items.

Saves about ~2 hrs per week

What it does

  • Watches threads that grow past a length you choose
  • Summarizes the whole thread with the current decision
  • Lists open action items with who owns them
  • Posts the summary to the thread so latecomers catch up fast

How it works

  1. Thread passes your length threshold
  2. AI reads all messages and produces summary + actions
  3. Summary posted as a reply or saved to a notes doc
  4. New people in the thread read the summary before reading back

What's included

  • Thread threshold setup
  • Summary prompt
  • Dedupe scheduling

Set it up yourself

Follow these 4 steps in order. You will need accounts for: Gmail.

Step 1: Choose your threshold and watch scope

  1. Decide what counts as a 'long thread' for you — 15+ messages is a common default.
  2. In Google Cloud, enable the Gmail API and create OAuth credentials (follow the inbox triage guide).
  3. Decide whether to watch all inbox threads or a specific label (e.g. Projects).
  4. Note your Gmail Apps Script quota: reading threads plus AI calls on each can add up — keep the label scope tight.

Watch out: Watching the entire inbox can cost significant API tokens per run; scoping to a label keeps it cheap.

Step 2: Build the summary prompt

  1. Create the prompt: 'Summarize this email thread for someone who just joined. 1) Current status/decision. 2) Open action items with owners. 3) Any deadlines. Under 250 words.'
  2. Instruct the AI to label items that are already resolved as resolved so they do not recur.
  3. Test on one old long thread and check the accuracy of the action list.
  4. Save as the SUMMARIZE prompt constant in the script or the HTTP Request body.

Watch out: Without the 'resolved' instruction the AI re-lists closed items forever — that defeats the purpose.

Step 3: Post to the thread

  1. Decide the delivery: a reply in-thread, or a dedicated Notes/Slack channel.
  2. In-thread: use the script to create a draft reply (never send automatically) containing the summary.
  3. If using a channel: extract the thread id + subject into the message so people can jump in.
  4. Only summarize threads that changed since the last summary (the script stores last-summarized timestamps in Script Properties or a sheet).
  5. Test: send 3 messages in a test thread, confirm the trigger fires once, not three times.

Watch out: Firing on every new message floods the thread — dedupe by storing per-thread last-summarized id.

Step 4: Set the schedule

  1. Add a time-based trigger in Apps Script running every 15-30 minutes.
  2. Add an error notification trigger so you learn immediately if it breaks.
  3. Run manually once and review the first generated summary.
  4. Iterate the prompt if the summaries feel too long or too short.

Watch out: Summaries that are shorter than the thread risk hiding nuance; review the first week manually before trusting it fully.

Frequently asked questions

What does the Email Thread Summarizer automation do?

Long threads collapse into a summary with the decision and the action items. Watches threads that grow past a length you choose

How much time does Email Thread Summarizer save?

It is estimated to save ~2 hrs per week. Actual savings depend on your volume.

Which tools does Email Thread Summarizer use?

It works with Gmail.

What does Email Thread Summarizer include?

Thread threshold setup, Summary prompt, Dedupe scheduling.

Can I set up Email Thread Summarizer myself?

Yes. The do-it-yourself guide on this page walks through 4 steps, from getting access to testing the finished automation.