Find the cheapest Hamburg–Copenhagen train with ChatGPT agent

Posted

Aug 4, 2025 by Ole Reissmann

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Last checked

Oct 16, 2026

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Method:

How we verify

Evidence: Article or interviewA newsletter, journalist or interview account of what happened.

Outcome

Asked (in German) to book the cheapest Hamburg–Copenhagen train for September, ChatGPT agent found a €63.26 fare after about ten minutes on the Deutsche Bahn site, then asked the author to log in; Comet was faster (3:40) but booked legs separately for €70.94.

Agent

ChatGPT agent

The source didn't share its exact prompt, so we wrote this from what it describes.

Run this task now, exactly as written below. Everything you need is here, so start straight away and only stop if something required is missing.

Goal: Find the cheapest train for my trip and get it ready to book.

Fill in before running: Which route and date, and any time-of-day limits?

What I'll give you:
- Route and date
- Rail account (I'll log in)
- Earliest and latest departure times
- Discount cards I hold

Rules:
- Compare through tickets with split tickets, on at least two booking sites, and pick the cheapest total for the same train.
- For each option, include departure time, travel time, number of changes and whether a seat reservation is included.
- Re-check the price just before you hand over, and give me the direct booking link.
- Show me the fare and stop at login or payment; I'll take over.

Output: The cheapest option with times, price and a link.

You'll know it worked when: I see the lowest total fare for that connection.

Run this task now, exactly as written below. Everything you need is here, so start straight away and only stop if something required is missing.

Goal: Find the cheapest train for my trip and get it ready to book.

Inputs (fill in or confirm):
- Route and date
- Earliest and latest departure
- Discount cards
- Rail account (I'll log in)
- Seat or class preference and luggage

Rules:
- Compare through tickets with split tickets and saver fares on the operators' sites.
- Include seat reservation costs.
- List the cheapest three with times and changes.
- Note ticket conditions (flex vs saver).
- Check whether a cheaper fare exists one or two departures earlier or later and say how much it saves.
- Flag tight connections under [MINUTES] minutes.
- Apply each discount card and show the price with and without it.
- Mention if the cheapest option needs a ticket for a specific train only (no flexibility).
- Show where the ticket will be delivered (app, PDF).

Checkpoint: Stop before payment.

If you get stuck: If a site needs login, ask. If a login, CAPTCHA or two-step code appears, stop and ask me to handle it; never guess or store passwords.

Verify before you finish: Recheck the cheapest fare on the booking page.

Output: Top three options and the booking page ready.

Done when: I can book the cheapest suitable train.

Source

https://olereissmann.com/i-tried-chatgpt-agent-and-perplexity-comet-to-actually-get-things-done/