Build an n8n AI Agent That Turns a Lawyer's Rough Notes into Time Entries

Step 1: Go to n8n.io

Time that isn't written down the same day is hard to bill. You jot a few words between calls, then rebuild the week from memory, and the short calls and quick emails go missing first. We are going to build an AI agent that turns your rough notes into time entries in a spreadsheet. First, you need an n8n account.

Step 2: Enter your email

This is just practice, so anything works — it won't actually send anything.

Step 3: Sign up

In the real n8n, it sends you a six digit code, then asks for a name, a password, and an account name. Go do that in your own browser later, then come back and we will build.

Step 4: Add credit first

Your agent needs a brain, and that means an API key from OpenAI. Go to platform dot openai dot com — that is the developer side, not ChatGPT, and it bills completely separately. Before you make a key, put some money on the account. A brand new key with a zero balance just returns errors. If you would rather not spend anything yet, n8n gives every new account free credits. In your own n8n, you can pick gateway credits on the model step and skip the key.

Step 5: Ten dollars is plenty

A little credit goes a very long way. You are charged per request, not per month, and writing a day of time entries costs fractions of a cent.

Step 6: Now the key

Balance sorted. Now go to API keys in the left menu.

Step 7: Create a secret key

Step 8: Name the key

Name it after whatever is going to use it. Future you, staring at a list of forty keys, will thank you. I am calling this one n8n agent.

Step 9: Create it

Default project, all permissions — that is fine for this. Create the key.

Step 10: Copy it now

Now pay attention, because this is the only time you will ever see this key. Copy it and paste it into n8n, or into your password manager. If you lose it, you do not get it back — you delete it and make another.

Step 11: Back to n8n

One last warning — this key can spend your money. Never commit it to code, never paste it into a chat, and if it ever shows up on screen while you are recording, revoke it before you publish.

Step 12: Start a new workflow

Now you are inside n8n. This overview page lists every workflow you have. Top right, click create workflow, and you land on an empty canvas.

Step 13: Add the first step

Every workflow needs a trigger — the thing that kicks it off. We want a chat trigger so you can paste in the day's notes.

Step 14: Trigger on a chat message

A panel slides in with every way a workflow can start — manually, on a schedule, on a webhook. We want on chat message, so we can have a conversation with the agent.

Step 15: Back to the canvas

n8n opens the node so you can configure it. There is nothing we need to change here, so close it with the X in the top right and get back to the canvas.

Step 16: Add the next node

Now we decide what happens when a message comes in.

Step 17: Open the AI nodes

A panel opens and asks what happens next. The agent lives under AI, right at the top.

Step 18: Add the AI Agent

There it is — AI Agent. This is the piece that can plan and then carry out actions using whatever tools you give it. You give it your notes, and it can write each time entry and save it to a spreadsheet — all in one step.

Step 19: Open the options

Right now this agent has no personality and no orders. It does not know it works for Calloway and Brandt, or what a good time entry looks like.

Step 20: Add a system message

Pick system message. This is the standing instruction the agent reads before every request. It is where we tell it who the firm is, how to write a time entry, and what it must never do.

Step 21: Write the system prompt

Here is the actual prompt. It tells the agent what each entry needs: the date, the matter, the hours, a one-sentence description a client can read, and a check for billing. A task with no clear matter gets marked unclear. And the rule that matters most: never invent, estimate or round your hours. If you didn't write the time down, the entry says so.

You are the time entry assistant for Calloway & Brandt LLP.

Calloway & Brandt LLP is a small litigation and business law firm. Its lawyers record their time every day, and the billing team turns those entries into client invoices at the end of the month.

The audience is the lawyer who wrote the notes, who reads every entry before it goes to billing.

The tone should be plain, brief and factual, like a billing description a client can read.

Your job is to turn the lawyer's rough notes into one time entry per task.

For each task, return:
- Date
- Matter (the client or case name exactly as the notes give it)
- Hours (exactly as written in the notes, or "Hours not given")
- Description (one sentence, starting with a past-tense verb, like "Drafted..." or "Call with client re: ...")
- Check: "Ready", or one short sentence on what the lawyer must confirm before billing

If the matter is unclear or a task could belong to more than one matter, write "Unclear" in Matter and say why in Check.

When the user asks you to save the entries, use the Google Sheets tool to store each one.

Never invent, estimate or round hours. Never add facts, results or legal conclusions that are not in the notes. Never include Social Security numbers, account numbers or other personal identifiers.

Step 22: Back to the canvas

That gives the agent everything it needs to know about writing time entries for the firm. Close the node.

Step 23: Give the agent a brain

See that red triangle on the agent? It is complaining because it has no model. An agent can plan, but it cannot think without a language model underneath it.

Step 24: Pick OpenAI

OpenAI chat model. This is where that API key finally gets used.

Step 25: Open the credentials

And here is where that key you copied finally goes.

Step 26: Create a new credential

You want create new credential, right at the bottom. In your own n8n, if you skipped the key, you would pick gateway credits here instead.

Step 27: Paste the key

This is the one moment it matters that you copied it — remember, OpenAI never shows it to you again.

Step 28: Save the credential

n8n tests the connection straight away, and from now on this credential is available to every node in every workflow — you only do this once.

Step 29: Open the model list

Now the model dropdown.

Step 30: Choose the model

GPT five mini. Fast, cheap, and plenty for turning notes into time entries. Do not reach for the expensive model until you have a reason.

Step 31: Back to the canvas

That is the brain wired in. Close it up.

Step 32: Add memory

Next, memory. Without this, every message starts from nothing — you could not say save those, because it would not remember which entries you meant.

Step 33: Simple Memory

Simple memory is fine here — it keeps the recent conversation inside n8n, no database, no extra credentials.

Step 34: Back to the canvas

n8n opens simple memory so you can set it up. The defaults are fine. It keeps the last five messages. Close it with the X.

Step 35: Add a tool

And now the good part — tools. This is what separates an agent from a chatbot. A chatbot just talks. An agent does things. We are going to give it Google Sheets so it can save every entry into a time log your billing team can work from.

Step 36: Search for Sheets

Google Sheets is not in the recommended tools, so search for it.

Step 37: Add Google Sheets

Google Sheets tool. Now the agent can write rows into a real spreadsheet, with columns matching what the system prompt tells it to return. When you say save those, each task becomes a row.

Step 38: Back to the canvas

Before we set this up, we need to actually create the spreadsheet. Close this node for now — we are going to hop over to Google Sheets and make one.

Step 39: Open Google Sheets

Switch to Google Sheets. You need to create the spreadsheet that this node will write to.

Step 40: Name the spreadsheet

First, name it so you can find it later.

Step 41: Type the first column header

Now set up the column headers. These need to match what the system prompt tells the agent to return. In A1, type Date.

Step 42: Matter

B1 — Matter.

Step 43: Hours

C1 — Hours.

Step 44: Description

D1 — Description.

Step 45: Check

And E1 — Check. Five columns, matching exactly what the system prompt tells the agent to return. Each task becomes a row in this sheet.

Step 46: Back to n8n

The spreadsheet is ready. Switch back to n8n and connect the Google Sheets node to it.

Step 47: Open the Sheets node

Double click the Google Sheets node to open it back up. Now we can connect it to the spreadsheet we just made.

Step 48: Add a credential

Now we need to connect this to a real Google account.

Step 49: Create a new credential

Create new credential — this one uses Google OAuth instead of an API key, so it is going to open a sign-in window.

Step 50: Sign in with Google

This opens the Google account chooser so you can pick which account to connect.

Step 51: Choose your account

Pick the Google account you want n8n to use. This is the account that owns the spreadsheet.

Step 52: Allow Sheets access

Google is asking what n8n is allowed to do. Check the first box — this lets n8n read and write your spreadsheets.

Step 53: Allow Drive access

Second box — n8n needs Drive access so it can find your spreadsheets by name.

Step 54: Allow external service

Last one — this lets Google connect to n8n as an external service. Check it.

Step 55: Sign in

All three checked.

Step 56: Pick the operation

Now we tell the node what to do. By default it reads rows, but we want to add rows.

Step 57: Append Row

Append row. Every time entry the agent writes gets added as a new row at the bottom of the sheet.

Step 58: Choose the spreadsheet

Now pick the spreadsheet.

Step 59: Daily Time Log

Daily Time Log — the sheet we set up with columns for the date, the matter, the hours, the description, and the check.

Step 60: Pick the sheet tab

Now pick which tab inside that spreadsheet.

Step 61: Sheet1

Sheet one — it is the only tab, so this is simple.

Step 62: Map the Date column

Now the columns. Each column has a purple button — click it and the AI agent figures out what data goes there.

Step 63: Map the Matter column

Matter. Same thing — click the purple button.

Step 64: Map the Hours column

Hours.

Step 65: Map the Description column

Description.

Step 66: Map the Check column

And check. Each one is now set to defined automatically by the model — the agent reads your column headers and figures out what goes where.

Step 67: Back to the canvas

The sheets tool is fully wired up — credential, operation, spreadsheet, sheet, and column mapping. Close it and let us test this thing.

Step 68: Open the chat

Everything is connected. Time to see if it works.

Step 69: Paste today's notes

Give it today's notes the way you actually write them: a few words per task, two matters, one task with no time and one with no clear matter.

Log my time for Oct 19. Harlow Foods v. Brightway Logistics: 1.2 drafting our responses to their second set of interrogatories, and 0.4 on a call with Dana Harlow about collecting the shipping records. Pemberton Estate: reviewed the draft trust amendment, forgot to track the time. Also 0.3 emailing opposing counsel to move the Kessler deposition.

Step 70: Send the message

Send it off. The agent reads your system prompt and turns each task into one entry, with the matter, your hours exactly as written, a clean description, and a check.

Step 71: Save to the sheet

Four entries. Two are ready to bill. For the trust amendment, it didn't guess the time. It says hours not given. And it couldn't tell which case the Kessler deposition belongs to, so it asks you to confirm. Now tell it to save them. This is where the Google Sheets tool kicks in.

Step 72: Send it

Send it. The agent uses the Google Sheets tool to write each entry as a row — date, matter, hours, description, and check.