When creating or redesigning a website, the project brief (cahier des charges) is the first deliverable to produce. This document formalizes the project's functional and technical requirements, and serves as the contractual reference between stakeholders (client, project manager, development team, vendors). This article details the role of the project brief, its content, and how to write one in a structured way.

Why is a project brief important?

The project brief — also referred to as "functional specifications" — is the reference document that describes all the requirements of a web project. It covers the functional scope (what the site must do), the technical constraints (how it must do it), and the delivery conditions (budget, schedule, resources). All stakeholders refer to it throughout the project's life cycle.

Why a project brief is essential

  • Scope framing: The project brief precisely defines the project's scope, reducing the risk of scope creep and aligning stakeholder expectations.
  • Centralizing requirements: It groups objectives, functional specifications, technical constraints, and acceptance criteria into a single document, ensuring overall consistency.
  • Anticipating risks: By identifying technical constraints, dependencies, and complexity points upstream, the project brief enables preventive actions before development starts.
  • Common reference: Whether for an internal team or an external vendor, the project brief is the shared reference that prevents ambiguity and divergent interpretations.

Key elements of a website project brief

An effective project brief covers all dimensions of the project. Here are the essential sections to structure.

Project objectives

State the site's objectives in measurable terms, tying them to the key performance indicators (KPIs) that will evaluate the project's success. For example:

  • Primary objective: Increase the visitor-to-newsletter-subscriber conversion rate by 15% over 6 months.
  • Secondary objectives: Reduce the bounce rate by 10%, increase average cart value through the e-commerce module.

Target audience

Define the user segments you are addressing through personas — detailed profiles describing the demographic characteristics, online behaviors, and functional needs of each target group.

Elements to document:

  • Demographic data: age range, geographic location, sector.
  • Functional needs: quick access to information, simplified purchase journey, mobile compatibility.

This analysis directly drives UX, information architecture, and content strategy decisions.

Functional specifications

List the expected features exhaustively, specifying the business rules and acceptance criteria for each. Examples:

  • Contact form with client-side and server-side validation, email notification to the administrator.
  • Online booking system with slot management and automatic confirmation.
  • Integration of a marketing automation tool (Mailchimp, Brevo) or a CRM (HubSpot, Salesforce).

Each feature must be described in enough detail for the technical team to estimate and develop it without ambiguity.

Technical specifications

Document the technical constraints and choices that frame delivery:

  • Hosting: shared, dedicated, or cloud infrastructure (AWS, OVH Cloud).
  • Compatibility: responsive design compliant with W3C standards, support for target browsers (Chrome, Firefox, Safari, Edge).
  • Tech stack: CMS (WordPress, Drupal), framework (Next.js, Laravel), programming language(s).

These specifications allow the development team to assess technical feasibility and estimate effort (in person-days or story points depending on the methodology used).

Design and user experience (UX)

Define the user interface (UI) and user experience (UX) requirements:

  • Graphic guidelines: color palette, typography, iconography, style guide.
  • Ergonomic principles: visual hierarchy, navigation architecture, accessibility (RGAA or WCAG compliance).

A structured design and an optimized UX have a direct, measurable impact on conversion and retention rates.

Budget and schedule

Define the budget envelope and the projected schedule, identifying the project's key milestones:

  • Budget: Breakdown by item (design, development, hosting, SEO, maintenance). Plan a contingency margin (typically 10 to 15% of the total budget).
  • Schedule: Schedule with validation milestones: kickoff, mockup delivery, functional acceptance (UAT), go-live, warranty period.

Practical tips for writing an effective project brief

Favor precision and conciseness

A project brief must be detailed enough to eliminate ambiguity while remaining readable. Use factual phrasing, structured lists, and verifiable acceptance criteria for each requirement.

Involve all stakeholders

Hold scoping workshops with the various profiles concerned: management, marketing, technical team, end users. This collaborative approach ensures the project brief covers all the project's needs and constraints.

Build on existing references

Use proven project brief templates or specification frameworks (such as the IEEE 830 standard for software specifications) to structure your document. This speeds up writing and reduces the risk of omissions.

Review and update the document

The project brief is a living document. In an Agile approach, it evolves through sprints and user feedback. Set up a change request process to track and validate every modification to the initial scope.

What are the next steps?

Once the project brief has been finalized and validated by all stakeholders, it becomes the reference document for the entire duration of the project. It serves as the basis for effort estimation, sprint or phase planning, and progress tracking. Share it with your team or vendors to officially launch the design phase.