Why this matters
A law firm sells time, and time that isn’t written down the same day is hard to bill. Lawyers jot a few words between calls and court, then rebuild the week from memory on Friday. The short calls and quick emails are the first to go missing.
Vague entries cost money too. A client who reads “work on file, 1.2” asks what they paid for, and the billing partner spends month-end chasing lawyers for descriptions and missing hours.
In this module you build an AI agent in n8n that turns a day of rough notes into one time entry per task: the matter, the hours exactly as you wrote them, a one-sentence description a client can read, and a check that tells billing what still needs you. It saves every entry to a Google Sheet, and it never fills in time you didn’t track.
What you’ll build
An n8n workflow with a chat trigger, an AI Agent with a system prompt for Calloway & Brandt LLP (a made-up law firm), an OpenAI chat model, memory and a Google Sheets tool, plus a Daily Time Log sheet with five columns: Date, Matter, Hours, Description and Check.
You paste in one day of rough notes across two made-up matters and get four entries: two ready to bill, one marked “Hours not given” because the time wasn’t tracked, and one marked Unclear because the notes don’t say which case the Kessler deposition belongs to. Then the agent saves all four as rows.
What you need
- Nothing to start the practicen8n, OpenAI and Google Sheets are practice copies. No account is created and nothing is billed.
- An n8n account, to do it for realn8n Cloud has a free trial, or you can self-host. The steps are the same.
- An OpenAI API key with a little creditWriting a day of time entries costs fractions of a cent.
- A Google accountFor the Daily Time Log sheet. n8n asks you to sign in to Google once.
- Your firm’s billing rules and data policyThe time increment you bill in, how descriptions must read, and whether client information may go into outside tools. The system prompt in the download is a starting point.
Concepts
3 ideas you’ll use in the practice.
The system prompt is the billing guideline
It says who the agent works for, who reads its output, and exactly what one entry looks like: date, matter, hours, a one-sentence description that starts with a past-tense verb, and a check.
The check column is what makes the sheet useful at month-end. “Ready” rows go straight to billing; every other row says in one sentence what the lawyer must confirm.
Never invent, estimate or round hours
The most important rule in the prompt: the hours come from your notes, exactly as written. If you didn’t record the time, the entry says “Hours not given” instead of a guess that ends up on a client’s invoice.
The same goes for facts. The description says what you did, not what it achieved, and adds nothing that isn’t in the notes. Your firm’s increment and narrative rules still apply when you review the row.
Memory and the Sheets tool make it an agent
Memory lets you say “save those” after the agent writes the entries, and it knows which ones you mean. The Google Sheets tool lets it write the rows itself.
Without them, it is a chatbot that tidies text you then copy by hand. With them, your time log fills in the same day.
Practice
Do every step yourself in a practice copy of the real tool. It checks your work, and “Do it for me” finishes any step you get stuck on.
Do it for real
Now repeat it in your own account. Tick each step as you go.
Downloads
- Time entry agent system prompt (.txt)The system prompt, the five column headers and the sample notes from the lesson.
Quick check
3 questions to check you’ve got it.
1. Your notes say “reviewed the draft trust amendment, forgot to track the time.” What goes in the Hours column?
- A typical amount for that task
- “Hours not given”, and the Check says to add the time
- 0.1, the smallest increment
Show the answer
“Hours not given”, and the Check says to add the time. The prompt says never invent, estimate or round hours. A guess would end up on the client’s invoice.
2. The notes mention an email about the Kessler deposition but don’t say which case it is in. What does the agent do?
- Puts it under the first matter in the notes
- Marks the Matter as Unclear and asks you to confirm
- Leaves the task out
Show the answer
Marks the Matter as Unclear and asks you to confirm. Billing time to the wrong client is worse than a question. Unclear, with a reason, is the safe entry.
3. Why does every entry have a Check column?
- Google Sheets needs five columns
- So billing can send “Ready” rows straight through and see exactly what to fix in the rest
- To store the client’s approval
Show the answer
So billing can send “Ready” rows straight through and see exactly what to fix in the rest. The check turns month-end chasing into a short list of rows that need the lawyer.
You reached the end of AI for Law Firms
Your time now goes in the same day, with nothing guessed. Pick your next course, or point the same agent at your own notes tonight.
Pick your next course →