Describe It Well: Prompts That Produce Working Code

📘 Vibe Coding Course · Lesson 3 of 6

The quality of AI-written code depends mostly on the quality of your description. Here is a template that works.

The six-part description

1. Goal — one sentence: what problem does this solve?
2. Input — file type, where it is, a sample.
3. Output — exact file name, columns, format.
4. Rules — every business rule, written as a list.
5. Examples — 2–3 input rows and the output you expect.
6. Done when — how you will check it.

Before

Make a script to clean my vendor file.

After

Goal: clean the monthly vendor export so it can be loaded into Tally.
Input: sample/vendors.csv (UTF-8, comma separated, header row).
Output: output/vendors_clean.csv with columns Name, GSTIN, State, Phone.
Rules:
- Trim spaces; Name in Title Case.
- GSTIN: 15 characters, uppercase; if invalid, keep it but add "CHECK" in a new Remarks column.
- State: derive from the first two digits of GSTIN (27 = Maharashtra, 07 = Delhi, ...).
- Phone: digits only, keep the last 10.
- Remove exact duplicate rows; keep the first.
Example: " acme traders ","27aapfa1234b1z5",... -> "Acme Traders","27AAPFA1234B1Z5","Maharashtra",...
Done when: running it on sample/vendors.csv gives exactly expected/vendors_clean.csv.

The second prompt takes three minutes longer to write and saves an hour of back-and-forth.

When something is wrong

Be specific and give evidence:

• Bad: “It doesn’t work.”
• Good: “Row 14 (Sharma & Sons) has State blank but GSTIN starts with 09 — that should be Uttar Pradesh. Fix the lookup and add a test for it.”

Ask for explanations

After it works, ask: “Explain what this script does in 8 bullet points, for a non-programmer.” If the explanation surprises you, you have found a bug in the requirements or the code.