Keep team system prompts from drifting week to week

What belongs in a system prompt

Keep the frozen prior short:

• Who we are (one or two lines)
• Voice (clear, calm, local; words to avoid)
• Hard rules (never invent prices; mark gaps as [NEED]; no medical/legal advice)
• Output shape defaults (short paragraphs; one ask)

Keep out of the system prompt:

• Today’s customer facts
• This week’s campaign
• One-off experiments
• Secrets, API keys, or private URLs

Today’s job belongs in the user message. Mixing them is how a style adjective starts inventing a policy.

One source of truth

Pick a single place the team can open without hunting:

• A short doc in your shared drive, or
• A pinned message plus a linked file, or
• A private repo file if you already live in git

Name it with a version: voice-and-rules-v3.md. Retire v2. Do not keep “final-final-USE-THIS.”

Rule: if it is not in the approved file, it is not the team system prompt.

Change control that takes five minutes

When someone wants a change:

1. Propose the exact lines to add or remove
2. Name the job that broke (example email, not vibes)
3. Owner approves or rejects in one sitting
4. Bump the version number
5. Everyone refreshes their saved custom instructions / system field from the file

No silent edits. Drift loves silent edits.

Split “voice” from “job kits”

Two layers beat one mega-prompt:

1. System / voice file — stable for months
2. Job kits — quote follow-up, review reply, meeting decision log — shorter recipes that call the voice file

People can improve a job kit without rewriting company voice. That is how you get speed without weekly rewrites of the constitution.

Test before you ship a new version

Run three real examples from last week through old vs new:

• Did invented facts go up or down?
• Did length explode?
• Would you still send it after a desk read?

If the new version is only “nicer,” keep the old one. Niceness without control is how discounts appear.

Onboarding and offboarding

New hire day one:

• Link to current version
• Two example good outputs
• Red list of data not to paste

Someone leaves:

• Rotate shared account passwords
• Confirm their personal system-prompt field is not the unofficial source of truth

Shadow prompts are still drift.

A monthly prompt hygiene meeting

Fifteen minutes on the first Monday:

• What broke in outbound drafts?
• Any [NEED] patterns the prompt should catch earlier?
• Any job kit that should be promoted or deleted?
• Confirm version number still matches what people actually paste

Cancel tools and prompts you do not use. Sprawl is a cost. Related: measuring AI ROI.

What not to do

• Do not paste a 2,000-word “company brain” into every thread
• Do not let five people maintain five conflicting voice blocks
• Do not change the system prompt mid-incident without a version bump
• Do not store secrets in prompts

Worked example (pattern only)

v2 says “never invent prices.” A teammate adds “be warm and generous.” Next week drafts start offering discounts. The fix is not a longer vibe paragraph. Revert the generous line, bump to v3, and add a job-kit rule: discounts only when the user message includes an approved offer code. Version control beats vibe control.

How a five-person team runs this week

Export whatever people currently paste as “the voice prompt.” Diff them. Pick one, label it v1, and delete the rest from pinned chats. Run three real drafts through v1. Schedule the monthly hygiene block. Drift stops when duplicates die.

Short close

One owned file, version bumps, job kits on the side—that is how team system prompts stop drifting.