Lab: build the month-end

In this lab you build a smaller version of the firm's setup, with twenty-nine sample lines in place of 3,400. You make a project and a skill, run the job, check it, and approve it. Then a late bank line arrives. You fix it the old way first, to see what goes wrong, and then you run the job again.

Read first. Read the story up to The run. Do the lab before you read Wednesday morning, if you can. Then you meet Wednesday yourself.

A free plan is enough. You need the Claude desktop app. The web version works too. Projects, skills, docs and decks are on every plan.¹,²,³ Three steps are marked paid plan: a sheet, a folder on your computer and a real scheduled task. Each has a free path beside it. A free plan has usage limits: if you reach one, wait and go on later. The editors have not yet run the free path from start to finish, so tell us if a step does not work as written.

Two levels. The core lab (Parts 1 to 8, on any plan) practises a project, a skill, one reproducible calculation, several pieces and your own tests. The full lab adds the three paid plan steps: a sheet, a folder on your computer, and a real scheduled task that reads its files from a connected drive. Only the full lab shows that the whole setup in the story works.

Lab at a glance

The core path is Parts 1 to 8. The times add up to 75 minutes. Allow up to 110 the first time, most of all if you have never made a skill. Keep your answers in a plain text file called lab-notes.md (or lab-notes.txt), or on paper.

Your app may look a little different. The names of buttons change from time to time. If you cannot find one, ask Claude in any chat, for example: "Where do I add instructions to a project?" Claude can usually tell you where a button is.

Part 1. Make the two files (10 minutes)

These are Lakeshore's last few days of September. The figures are made up. Both the bank and the ledger start the week at $186,000.00. This is the money in the account before these lines. The dates differ by a day or two for the same payment, because the bank often records a payment after the company does.

The bank's lines. Save them as bank-september.csv. Two deposits of $2,000.00 have no name. Banks sometimes leave the name out.

date,type,name,amount
2027-09-24,Deposit,Parma Hardware,4210.00
2027-09-24,Check 2291,Great Lakes Freight,-1860.50
2027-09-27,Deposit,Lorain Builders,5125.25
2027-09-27,Check 2292,Ohio Edison,-940.75
2027-09-28,Deposit,,2000.00
2027-09-29,Deposit,,2000.00
2027-09-28,Deposit,Erie Street Diner,3450.00
2027-09-28,Check 2293,Summit Packaging,-2315.00
2027-09-29,Deposit,Medina Farm Supply,2890.00
2027-09-29,Check 2294,Payroll service,-6480.00
2027-09-30,Deposit,Akron Tool Rental,7926.00
2027-09-30,Bank fee,Monthly fee,-525.00

The ledger's lines. Save them as ledger-september.csv. The last five lines are the ones the bank has not shown yet.

date,type,name,amount
2027-09-23,Deposit,Parma Hardware,4210.00
2027-09-22,Check 2291,Great Lakes Freight,-1860.50
2027-09-24,Deposit,Lorain Builders,5125.25
2027-09-24,Check 2292,Ohio Edison,-940.75
2027-09-27,Deposit,Bay Village Bakery,2000.00
2027-09-28,Deposit,Solon Garden Center,2000.00
2027-09-27,Deposit,Erie Street Diner,3450.00
2027-09-27,Check 2293,Summit Packaging,-2315.00
2027-09-28,Deposit,Medina Farm Supply,2890.00
2027-09-28,Check 2294,Payroll service,-6480.00
2027-09-29,Deposit,Akron Tool Rental,7926.00
2027-09-30,Bank fee,Monthly fee,-525.00
2027-09-29,Deposit,Canton Plumbing,4000.00
2027-09-30,Deposit,Elyria Motors,2120.00
2027-09-28,Check 2295,Northcoast Insurance,-5000.00
2027-09-29,Check 2296,Lake Erie Lumber,-2800.00
2027-09-30,Check 2297,City of Cleveland,-1500.00

To make each file:

1. Open a plain text editor. On Windows, use Notepad. On a Mac, use TextEdit, and choose Format, then Make Plain Text.
2. Paste the lines, with the first line date,type,name,amount.
3. Save the file with the name above, ending in .csv. If your editor adds .txt, change the name back.

Or paste the lines into a chat and ask Claude: "Give me this as a file called bank-september.csv." Then download the file.

Put both files in a new folder called Lakeshore.

Part 2. Build the setup (15 minutes)

The project.

1. In the Claude desktop app, open Projects in the menu on the left, and make a new project called "Lakeshore month-end".
2. In the project, find the place for files, and add your two .csv files. You should see both file names in the project.
3. Find the project's instructions, and paste the text below. Save it.

You prepare the month-end pack for Lakeshore Supply. The bank's lines and the ledger are in this project's files. Use the newest bank file. Both start at $186,000.00.

Match each bank line to a ledger line with the same amount and a date no more than five days apart. Use the name or check number too, where there is one. If a bank line could match more than one ledger line, pair it with one, and list the pair under Needs a look. List every line that has no match. Work out reconciled cash: the bank's closing balance, plus deposits the bank has not shown yet, minus checks the bank has not paid yet.

The pack is three pieces: the numbers doc, the memo, and a deck of three slides. Slide 2 shows reconciled cash and the bank's minimum, side by side. Slide 3 lists the timing items and any unrecorded items. The bank's minimum is $195,000.00.

After every run, write a run note: the files you read, the lines matched, the lines left over, reconciled cash, and the pieces you made or updated.

Never send anything. If the bank and the books do not agree, say so in the first line.

Paid plan, optional. In the desktop app, let Claude read your Lakeshore folder (ask Claude: "How do I let you read a folder on my computer?"), and change the sentence "The bank's lines and the ledger are in this project's files" to name your folder. Then Claude reads your files where they are.

The skill.

A skill needs code execution turned on. Code execution lets Claude run small programs.²

1. Open Settings, then Capabilities. Make sure code execution is turned on.
2. Start a new chat, outside the project. Type: "I want to make a skill called month-end memo. Here are its rules." Then paste these five rules:

Month-end memo. Use this when asked for a month-end memo.

1. The first line is the status. Write READY when reconciled cash is the same as the cash in the ledger and nothing is unrecorded. Write NOT READY when anything is unrecorded.
2. A timing item is in the ledger and not yet at the bank. Count timing items. Do not list them.
3. An unrecorded item is at the bank and not in the ledger, such as a returned check. List each one under the status, with its date and amount.
4. Then give reconciled cash, and how far it is above or below the bank's minimum.
5. Never write that the books are correct. Write what was compared, and what was the same.

3. Answer Claude's questions. When Claude has written the skill, follow its prompt to save it. If you see no prompt, ask: "Save this skill for me."
4. Open Settings, then Capabilities, then Skills, and turn the new skill on.⁴

If you cannot make a skill, paste the five rules at the end of the project's instructions. The lab works the same way.

In lab-notes.md, write one line for each part you built: what it is for.

Part 3. Run the job (10 minutes)

Start a new chat inside the project. Type one request.

Prepare the September 2027 month-end pack. Match the lines with a program if you can. Make the numbers as a doc with a table, the memo as a doc and the slides as a deck.

On a paid plan, you can ask for the numbers as a sheet.

When Claude has finished, write in lab-notes.md:

1. How many pairs did it match? Which lines were left over? Which lines did it list under Needs a look?
2. What is reconciled cash?
3. What does the memo's first line say?
4. The time the run took. Note the clock time when you send the request, and when Claude finishes.

If your figure is not what you expect, see If something goes wrong after Part 7.

Then tell the setup which pieces to update next time.

1. Open each piece. You find all three in the Artifacts tab in the menu on the left.
2. Click Share, and copy the piece's link. On a free plan you may not be able to share by link. Then write down the piece's exact name, the title shown at the top of the piece, instead. If Claude still makes new pieces later, that is a finding for Part 8. Then keep a short current-version list in the instructions: each piece, its link or name, and the date of the run that made it.
3. Add the three links, or names, to the project's instructions, under a line that says: "Update these pieces. Do not make new ones."

Part 4. Test and approve (10 minutes)

Do these five tests. Do not use Claude for them.

1. The source balance. Add the bank's twelve lines to $186,000.00 with a calculator, from bank-september.csv itself. That is the bank's closing balance. Compare it with the closing balance Claude used. This test uses the bank's own file, not Claude's work.
2. The arithmetic. Work out reconciled cash, using the leftover lines Claude listed in Part 3. Your fourth test, below, makes sure those lines are right.
3. The matching. Choose three matched pairs, and find each one in your two files. Then find the two $2,000.00 deposits without a name. Could each one be matched to either ledger line? Did Claude list them under Needs a look?
4. The leftovers. Find each leftover line in ledger-september.csv. Is each one a deposit the bank has not shown yet, or a check the bank has not paid yet?
5. The pieces. Open the numbers doc, the memo and slide 2. Do all three show the same figure?

If something is wrong, do not fix the piece. Change the project's instructions and run the job again.

Then write your approval in lab-notes.md, with the date and time. It must name the pack and the figure. Use Nisha's message in The run as a model.

Save the memo as a PDF: open the memo, find its export option (in the Share menu or the menu next to it), and choose PDF. Name the file memo-1.pdf. This is what the client gets.

Part 5. Write the morning check (5 minutes)

Write the instruction for a scheduled task that checks the bank each morning. Write it in lab-notes.md. It must say:

• what to read,
• what to compare it with,
• where to report (in this lab, in the chat),
• and what it must not do.

Paid plan, optional. Turn it on as a scheduled task, and use Run now once.⁵ A task that runs in the cloud cannot count on a folder on your computer. Keep the files in a connected app, such as Google Drive, and name that place in the instruction.

Part 6. Wednesday: fix it by hand (5 minutes)

A message arrives.

"The bank's lines for September have changed. There is one new line, dated September 30: a returned check from Erie Street Diner, minus $3,450.00."

Open bank-september.csv in your text editor. Add this line at the end. Choose Save As, and name the new file bank-september-2.csv. The first file stays as it was.

2027-09-30,Returned check,Erie Street Diner,-3450.00

1. Work out the new reconciled cash yourself.
2. Now do what Hamza began to do. Open the deck from the Artifacts tab. Change the figure on slide 2 yourself. Or, in the chat where you made the deck, ask Claude: "Change only slide 2 to the new figure."
3. Open the other pieces. In lab-notes.md, list every place that is now wrong. Check the numbers doc, the memo and slide 3.

How many places did you find?

Part 7. Wednesday: run the job again (10 minutes)

1. Add bank-september-2.csv to the project. On the paid path, it is already in your folder.
2. Start a new chat inside the project.

The bank's lines for September have changed. Prepare the September 2027 month-end pack again, from bank-september-2.csv.

3. Do the five tests again.
4. Write a new approval. It must name the new figure and say that it replaces the first pack.
5. Save the memo as a PDF again, as in Part 4. Name it memo-2.pdf.
6. Write the message to Dana, in five sentences or fewer. Say what changed, why, the old figure, the new figure, and which pack to use.

In lab-notes.md, write the time the second run took, and the time your tests took.

If something goes wrong.

• Your figure is not $198,300.00 (or $194,850.00 in Part 7). Ask Claude: "Show me each matched pair and each line left over." Compare its list with the answers at the end of this page. Then change the instructions, not the pieces, and run again.
• Claude made new pieces instead of updating the old ones. That is a real finding. Write it in your notes. Check that the links or names are in the instructions, and run again.
• Claude did not use the skill. Check that the skill is turned on in Settings. Or paste the five rules at the end of the project's instructions.

Part 8. What did the setup do? (10 minutes)

Answer in lab-notes.md.

1. Make two lists: what the setup did, and what you did.
2. In Part 6 you fixed one slide. In Part 7 you ran the job again. Which was faster? Which left the pieces the same as each other?
3. Did Claude update your three pieces in Part 7, or make new ones? If it made new ones, what would you change in the setup?
4. Name one rule in your instructions that is only a sentence. What could make it a setting? (A setting is a permission in the app, such as which connected apps are turned on. A sentence only asks. A setting stops.)
5. Next month, October's files arrive. What exactly would you have to do?

Part 9. Decide as Nisha (stretch, 10 minutes)

Read Friday's decision. In ten lines or fewer, write what you would tell Walter: how far the setup may run alone, how you would charge, and one thing that could still go wrong with your answer, and who would catch it.

What to hand in

lab-notes.md, memo-1.pdf and memo-2.pdf.

How the lab is graded

The lab is worth 10 points.

Part 9 is not graded.

Check your answers

Part 3. Twelve pairs match. The two $2,000.00 bank deposits have no name, and each could be Bay Village Bakery or Solon Garden Center. A good run lists them under Needs a look. The figure is the same either way, but a person should confirm them with the bank. Five ledger lines are left over: two deposits, $4,000.00 and $2,120.00, which is $6,120.00, and three checks, $5,000.00, $2,800.00 and $1,500.00, which is $9,300.00. The memo's first line says READY.

Part 4. The bank's twelve lines add up to $15,480.00, so the bank's closing balance is $201,480.00. If Claude used another closing balance, your first test has caught an error.

That is $3,300.00 above the bank's minimum. The ledger's seventeen lines add up to $12,300.00, so the ledger's balance is $198,300.00 too. The two agree, which is why the status is READY.

Part 5. A good check says: read the newest bank file; compare its closing balance with the one in your last run note; report in the chat, or in the firm's channel; change nothing in the pack.

Part 6. The bank's closing balance is now $198,030.00, and reconciled cash is $194,850.00. After the fix by hand, slide 2 is right. At least five places are wrong: the numbers, the memo's first line (it still says READY), the memo's figure, the comparison with the minimum (it still says above), and slide 3, if it lists the items.

Part 7. The memo's first line now says NOT READY, with one unrecorded item: the returned check, $3,450.00. Reconciled cash is $194,850.00, which is $150.00 below the bank's minimum. The ledger still says $198,300.00, because Lakeshore's books do not show the returned check yet.

Part 8. A good answer to question 5: put October's two files in the project, or in the folder, and type one request. Then check, approve and send. If Claude made new pieces in Part 7, the links were missing from the instructions, or the run did not use them: say so in your notes.

What you practiced

You chose a part for each need, joined the parts into one setup, and ran a job with one request. You checked the result without the AI and approved it by name. When the figures changed, you saw what a fix by hand leaves behind, and you let the setup do the job again.