Does Claude do better when you give it your business notes?

With the notes of a made-up bakery, Claude used the right facts in 30 of 30 replies. Without them, in 0 of 30.

Does Claude know your business?

"Each Claude Code session begins with a fresh context window". Anthropic advises treating CLAUDE.md as "the place you write down what you'd otherwise re-explain".

What was tested?

We used a made-up bakery with 10 short notes. They cover prices, a refund rule, the sign-off, holiday hours, wholesale terms, staff, suppliers, social posts, allergens and gift cards. Ten tasks each needed facts that exist only in those notes, such as a wedding cake price or the flour order day. Claude Haiku did each task 3 times, in six setups. A reply passed only if it held every required fact.

What happened?

No notes: 0 of 30 replies passed.
The 10 notes written inside CLAUDE.md: 30 of 30.
The 10 notes as separate files, with a one-line index in CLAUDE.md: 30 of 30.
The same files with no index, only a line saying the folder exists: 30 of 30.
With 40 unrelated notes added, 50 in all, all in one file or as files with an index: 30 of 30 each.

What did it cost?

Average cost per reply was $0.0021 with the notes inside CLAUDE.md and $0.0024 with files and an index. Without an index it was $0.0029, with 3.2 tool calls instead of 1.6. At 50 notes both ways cost $0.0027.

What does it mean?

The notes mattered far more than how they were stored. At this size, one file worked as well as an index. A folder with no index still worked, at a higher cost. At 50 notes the file and the index cost the same.

How far can this be trusted?

One model, one made-up business and 10 tasks. The 40 extra notes were templated and unrelated.
Two of our checks were too strict and one was too loose. We corrected all three and regraded or reran the affected runs.
The tasks needed one or two facts each. Notes that conflict were not tested.

What we would do

Write down the facts you would otherwise re-explain: prices, rules, sign-offs, deadlines.
We would keep each topic in its own short note, listed in CLAUDE.md with one line each. In our test one file worked as well at 50 notes.
Test with a task that needs one of your own facts, with and without the notes.

Check

Pick one fact only your business knows, and ask for a task that needs it. The reply must use it.
This result covers one model and short notes.

Learn it step by step: How Claude remembers