We've received several hundred briefs over the years. The briefs that produce good work share a set of characteristics that have nothing to do with format and everything to do with what information is included. The briefs that produce poor work share a different set of characteristics, and almost all of them are the result of the same underlying problem: the brief was written before the internal conversation was finished.
This post is a guide to writing a brief that gives an agency everything it needs to do good work. It's also, inevitably, a guide to having the internal conversations that make that possible.
The six things a useful brief answers
1. What does success look like, specifically?
Not "better engagement" or "more conversions." What metric, at what threshold, by when? "Increase email-attributed revenue from £45,000/month to £65,000/month by Q4 2026" is a success criterion. "Improve our email programme" is not. If you can't define success in specific, measurable terms, the brief isn't ready.
2. Who are your customers?
Not a demographic description, a behavioural one. How do they buy? What triggers a purchase decision? What's the average purchase frequency? What's the lifecycle from first purchase to lapse? If you have customer data, share it. If you don't, say so, it tells the agency that one of the first pieces of work will be establishing that baseline.
3. What's already been tried?
Share your existing programme's performance data, flows, campaigns, key segments. Share what's been tested and what the results were. Share what's been discontinued and why. This context prevents the agency from repeating your mistakes and allows them to build on what's already working rather than starting from scratch.
4. What does the agency have access to?
ESP access level (read-only? full admin?). CRM data, what fields, what segments, how fresh? Website analytics. Design assets. Brand guidelines. The list of things a new agency needs access to is longer than most clients expect, and the sooner that access is provisioned, the sooner productive work starts. List everything in the brief rather than triaging it later.
5. What constraints exist?
Budget range (agencies calibrate the scope of their response to the budget available, not sharing it doesn't produce a better proposal, it just produces an inaccurate one). Legal constraints, any compliance requirements specific to your market or category. Brand constraints, what can and can't be done creatively. Technical constraints, integrations that are fixed, platforms that can't be changed.
6. What does the decision process look like?
Who approves work? How many rounds of revision are expected? What's the turnaround SLA on approvals? Agencies that don't know how decisions are made at the client either over-engineer their approval process (causing delays) or under-engineer it (causing rework). A brief that explains the decision chain produces a more efficient working relationship from day one.
The brief format that works
Length: two to four pages. A brief longer than four pages has usually not been edited, it's been expanded. Information that's buried in a long brief is functionally absent. Prioritise ruthlessly.
Format: document, not slide deck. Brief-as-deck forces the writer to summarise before the thinking is complete. The section structure that covers the above six questions, in order, is a reliable format.
Version: date it and version it. If the brief changes between issue and response, document what changed and why. Briefs that evolve without documentation produce responses that don't match the revised requirements.
What good agencies do with a brief
A brief should prompt a response, questions, clarifications, a challenge to the assumptions underlying the objectives. If an agency returns a proposal without any questions, they either have too much experience in your exact category (unlikely) or they haven't read the brief carefully enough to know what they don't know (more likely).
The pre-proposal questions are worth taking seriously. They are often a more reliable indicator of how the agency thinks than the proposal itself. The questions reveal what they prioritised, what they found ambiguous, and where their expertise is genuinely deep versus where it's being constructed for the response.
Good work starts with a good brief. The brief is your responsibility, not the agency's. Write it as if the quality of the outcome depends on it, because it does.