Why does my ChatGPT answer have buttons?

You are my careful tool builder: the friend at the table who builds the calculator everyone trusts. I have one everyday job I want to get done faster, and I want you to turn it into a small interactive tool I can use right here in the conversation: boxes I type into, buttons, sliders, a chart, a checklist or a map, whatever fits the job best. I will act on what this tool tells me (pay my share of a bill, buy the food, leave at a certain time), so a wrong total or a hidden assumption is worse than no tool at all. Getting it right and being open about every assumption comes first; looks come second.

RULES FOR THIS WHOLE CONVERSATION
- Never invent a number, price, rate, distance, time or fact I have not given you. If the tool needs one I have not supplied, ask me, or add a clearly labelled box for me to fill in, marked [I NEED THIS], and leave it empty.
- If you look something up on the web or a number comes from the map itself (a tax rate, a distance, a drive time, an exchange rate, an opening time), show the source and the date next to that number inside the tool, and let me edit it.
- Every calculation follows the rule I give you. If my rule is missing or unclear (for example, whether tip is worked out before or after tax), ask before you build. Never pick a rule silently.
- Round only the figures you show me, never the working, and say how you round (for example, to the nearest cent). If rounding leaves a shares total that is a cent or two off the real total, say so and show where the difference went.
- If an interactive tool is overkill for my job (I only need one number, a short list or a yes or no), say so and give me plain text instead.
- If you cannot show interactive elements in this chat, say so, then give me the same thing as a clear table plus the formula in plain words, so I can still use it.
- If a line in MY SET-UP still shows its bracketed example, treat it as not stated.
- If I paste a filled-in MY SET-UP after this prompt, use that one and ignore the template lines.

MY SET-UP (I fill this in once; any line can say "not stated")
- The job: [What you want to do and when, in one or two sentences. e.g. "Split the bill after dinner tonight for five friends; some of us shared dishes and two people did not drink" or "Plan the cooking for a roast for somewhere between 6 and 9 people, eating at 7pm" or "Compare three phones I am choosing between".]
- Who uses it and on what: [Just you, or a group passing one phone around? Phone or laptop? e.g. "me, on my phone, at the table, so big buttons and everything on one screen" or "me on my laptop, I will come back to it a few times this week". If a group is passing one phone round, put each person's result on its own line they can find without scrolling, and use first names or initials only.]
- My real inputs: [Paste or type what you already have. e.g. receipt lines with prices ("Pizza 18, Pasta 16, Salad 12, Burger 17, Garlic bread 6, Bottle of wine 30, tax 8.91"), a list of names, a starting amount, the stops on a trip, or the specs of the three products copied from the shops' pages. Write "not yet" if you want empty boxes to fill in yourself.]
- The rule: [How the maths or the plan should work, in your own words. e.g. "a shared dish is split evenly between whoever ticked it; tax is split in proportion to what each person ordered; tip is 15% of the total before tax" or "savings grow once a month at a rate I type in; ignore tax" or "nobody does the bins two weeks running".]
- Something I already know is true: [A tiny case you can check in your head, or a fact the tool must respect. e.g. "Two people, one 20 dish each, no tax, no tip: each pays 20" or "the lamb needs 2 hours in the oven plus 30 minutes resting" or "phone B's battery is 5000 mAh, it is in my paste".]
- What I will change while I use it: [The things you will want to fiddle with. e.g. "the tip percentage and who had which dish" or "the number of guests and the time we eat".]
- Currency and units: [e.g. "US dollars and miles" or "euros, kilometres and kilograms".]
- How it should look, if I care: [e.g. "one plain screen, no pictures" or "big and simple, my dad will use it". Write "not stated" and you choose whatever is clearest.]

WHAT KIND OF TOOL THIS IS
Decide which kind my job is, tell me in one line, and follow that branch. If it mixes two, use both.
- Splitting money between people: before building, ask how anything shared, tax, tip and fees are divided if my rule does not say. Check: every share added together equals the real total, to the cent, with any rounding difference shown.
- Growing or paying down money over time (savings, a loan, a mortgage payment): ask whether money goes in at the start or end of each period and how often interest is added, if I have not said. Check: with the rate set to 0, the total equals what I put in. Label the result as an estimate to learn from, never as a quote from a bank or lender.
- A timeline or schedule (cooking, a moving day, a weekly meal plan): work backwards from my fixed time. Check: every step finishes before the next one needs it, and no two steps need the same oven, hob, person or car at the same moment. If they clash, show the clash; never quietly move my fixed time.
- A route or map: every distance and drive time is an estimate, labelled with where it came from and the date. Check: the legs add up to the total shown.
- A comparison table: use only the specs I pasted. Any cell I did not give you says "not stated", never a figure from memory. Check: every number in the table can be found in my paste, and sorting by each column puts the rows in the right order.
- A rota, tracker or quiz: check that over one full cycle everyone gets a fair share of turns and nobody gets the same job twice in a row unless I said so. For a quiz, check that every answer matches the list I gave and nothing outside the list appears.

STAGE 1: ASK BEFORE YOU BUILD
Read my set-up. Ask me up to four questions, only ones whose answers would change the result or the format, and offer me choices where you can. e.g. "Is the tip worked out on the total before or after tax?", "Should the two people who did not drink pay nothing towards the wine?", "Do you want the stops on a map or as a list with drive times?". If The job or My real inputs is missing, ask for it. If "Something I already know is true" says "not stated", suggest one small case, tell me the answer you expect, and ask me to confirm it before you use it as a check. Then stop and wait for my answers. If my set-up already answers everything that would change the result, say "No questions" and go straight on.

STAGE 2: PICK THE FORMAT AND SAY WHY
In three lines or fewer, tell me the format you will use (for example: input boxes with a running total; a slider with a line chart; a map with a list of stops; a checklist with times; a side-by-side table I can sort; or plain text) and why it suits my job better than the other options. If plain text is the better answer, say so and give it instead of building anything.

STAGE 3: WORK IT OUT AND CHECK IT, BEFORE ANY TOOL
Write the formula or the plan in plain words. Then, under the heading CHECKED, run three cases through it and show the working line by line: the thing I already know is true, one ordinary case of your own, and one edge case (a zero, a single person, a very large number, or an item nobody ticked). For each case, work out the expected answer by a different route from the formula (add it up item by item, or count it out by hand), then give: expected, what the formula gives, and MATCH or NO MATCH. Also run the check for my kind of tool from WHAT KIND OF TOOL THIS IS. If anything is NO MATCH, fix the formula and run the cases again until everything matches.

STAGE 4: BUILD THE TOOL
Build it in this chat, using exactly the formula or plan that passed. If anything failed in Stage 3, say in one line above the tool what you fixed. Inside the tool, or directly under it, include:
- every input I said I will change, editable, with clear labels and units;
- the result, large and easy to read;
- a line headed HOW THIS IS WORKED OUT, giving the formula in plain words;
- a line headed ASSUMPTIONS, listing every rule, rate and default the tool uses, including any you chose yourself;
- a plain text summary of the current result that I can copy, because I will save the final numbers myself.

STAGE 5: HAND IT OVER
Finish with four short lines:
- CHECK THIS ONE BY HAND: the single number or step I should check myself before I act on it, and how to check it in under a minute.
- LEAST SURE ABOUT: the assumption or input you are least sure of, and why.
- ONE USEFUL CHANGE: one tweak that would make the tool better for my job, asked as a yes or no question.
- REBUILD PROMPT: a short prompt, in a copyable block, that rebuilds this exact tool with the same rules and my current inputs in a new chat.

WHEN I ASK FOR CHANGES
- Change only the part I point at, keep everything else exactly as it is, and run the CHECKED cases again after every change.
- If I say a number looks wrong, show the working for that one number line by line before you change anything, then tell me whether the rule or my input caused it.
- If my change would break the rule I gave you, tell me before you make it.
- If I say "plain text", drop the interactive parts and give me the result as a short list with the formula.

MY SET-UP (I fill this in once; any line can say "not stated")
- The job: Split the bill for five of us after dinner tonight: Ana, Ben, Chloe, Dev and Eli. Some dishes were shared, and Ben and Dev did not drink.
- Who uses it and on what: Me, on my phone, at the table, passing it round so people can see their own share. Big buttons, everything on one screen.
- My real inputs: Pizza 18 (Ana and Ben shared it); Pasta 16 (Chloe); Salad 12 (Dev); Burger 17 (Eli); Garlic bread 6 (all five of us); Bottle of wine 30 (Ana, Chloe and Eli). Food and drink total 99. Tax on the receipt 8.91. No tip on the receipt yet.
- The rule: A shared item is split evenly between the people who had it. Tax is split in proportion to what each person ordered. Tip is a percentage of the total before tax, split the same way as the tax. Ben and Dev pay nothing towards the wine.
- Something I already know is true: Two people, one had a 30 dish and the other a 10 dish, tax 10% of the bill, no tip: they pay 33 and 11.
- What I will change while I use it: The tip percentage (we usually choose between 15% and 20%) and who had which dish, in case I have remembered wrong.
- Currency and units: US dollars, rounded to the cent.
- How it should look, if I care: Plain and readable in a dark restaurant. One line per person with their total, and a grand total at the bottom that should match the receipt plus tip.