Writing good prompts

A prompt is your message to the model. The model knows nothing about your company, your clients or the purpose of your request. Whatever you leave out, it fills with generalities or, worse, with plausible-sounding assumptions. The examples on this page come from the fictional Kieselmatt Treuhand AG, a Swiss fiduciary firm.

The five building blocks

Not every message needs all five. But when a result misses the point, one of them is almost always missing.

Example 1: An email to a client

Before

Write an email to Brunner about the missing documents.

What comes back is a polite, generic email with no concrete list and a deadline the model picked itself.

After

I work at Kieselmatt Treuhand AG. Write an email to Mr Marco Brunner, managing director of Holzwerk Brunner GmbH.

For the 2025 annual accounts we are still missing: the December bank statements, the inventory as at 31 December and the lease agreements for the two delivery vans. We need the documents by 15 October so the accounts are ready at the end of October.

Tone: friendly and firm, formal address. British spelling. At most 120 words, the missing documents as a bulleted list. No sign-off, I will add it myself.

Better, because the recipient, the concrete list, the deadline with its reason and the format are all settled. The model does not have to guess anything.

Example 2: Comparing two documents

Before

Summarise this: (followed by 20 pages of pasted text)

Pasted text loses tables and lists, and "summarise" does not say what for.

After, with the files "Expense Policy 2025" and "Expense Policy 2026" attached:

Attached are our Expense Policy 2025 and Expense Policy 2026. Create an overview of the changes for our staff.

Format: a table with the columns topic, before, now and section in the 2026 policy. Then at most three sentences on what to watch out for day to day. Only include what the two documents say. If a rule is worded unclearly, say so.

Better, because the sources are complete, the purpose is clear and the "section" column makes every statement checkable.

Example 3: Preparing a decision

Before

Leasing or buying, which is better?

After

Bäckerei Mehlwerk GmbH needs a new delivery van for about CHF 58,000. The options are buying with a bank loan or leasing over 48 months. I am preparing a meeting with the management.

First ask me up to three questions about information you need for a fair comparison. Then: a table with the pros and cons of both options and a list of the assumptions I need to clarify with the client. Only calculate with figures I give you.

Better, because the questions stop the model from inventing interest rates or residual values, and the result goes straight into the meeting.

Keep working in the same chat

The first result is a draft. Improve it with short follow-up instructions, because the model knows the conversation so far:

• "Shorter, at most 80 words."
• "The inventory has already arrived. Remove it from the list."
• "More formal, no exclamation marks."
• "Turn this into a Word file."

Three things help:

• If your first message went wrong, fix it with Edit and resend instead of adding corrections. That keeps the conversation clean.
• If you want a second opinion from another model, pick it in the model menu and regenerate the last answer with it.
• When a new topic starts, open a new chat with New chat. The model reads the whole conversation with every message, so a long chat costs more credits and eventually reaches the limit of what the model can process at once.

Files instead of pasted text

Attach documents with Add (the plus in the message box) and Attach file, or drag them into the chat. Files have several advantages over pasted text:

• The file stays available for the whole chat. Ten messages later you can still ask about it.
• Tables, lists and sections are preserved.
• Custodos can edit Word, Excel and PDF files directly instead of only returning new text. See Creating and editing documents.
• Sensitive details in attachments are checked just like your message.

If you need the same documents again and again, put them in a brain instead of attaching them every time. See Building a good brain.

Order the format

• Table: "as a table with the columns client, deadline, status". Every table in an answer offers Copy table and Download table.
• File: "as a Word file", "as an Excel file with formulas", "as a PowerPoint with five slides". The file appears below the answer for download.
• Variants: "three subject line suggestions, each at most eight words".
• Length and language: a number of words or sentences instead of "short", plus the form of address and the spelling.

Have facts checked, and check them yourself

• Current information such as prices, company details or new regulations is often beyond what a model knows. Use Web search in the message box and open the sources it lists. See Web search.
• Internal information belongs in a brain. Answers from it name the documents they rely on, and you can open each one.
• Figures need recalculating. For spreadsheets, have formulas written into the file so Excel does the maths. See Spreadsheet analysis.
• Make gaps visible: "Mark every statement that does not come from the attached documents."

Reuse good prompts

• Project: A project's instructions apply to every chat in it, for example language, form of address and your area of work. Projects belong to you personally. See Projects.
• Agent: A task the team does regularly becomes an agent with fixed instructions and conversation starters. See Building good agents.
• Shared chat: A successful chat is the best example for colleagues. See Sharing and finding chats.

Before you send

• Does the model know who the result is for?
• Is the material attached or the right brain turned on?
• Does it say how long and in what form?
• May the model ask instead of guessing?

Frequently asked questions

Next steps