What is a Communication Codex?
A Communication Codex is a comprehensive brand voice document we create for every client. It captures who they are, how they talk, what they care about, what to never say about them, and how to write for them across every channel.
The Codex is the single source of truth for how we write for a client. When it's good and up to date, Claude can produce copy that sounds like it was written by someone who's been working on that account for years. When it's stale or missing, Claude sounds generic. Which is why keeping it current matters so much.
The Codex pipeline
(Google Doc)
Claude Project
context always
What's in a Codex? Walk through the sections.
The Codex template has five main sections. Here's what goes in each one and why it matters for Claude.
Mission, vision, values, and personality descriptors. This is the "who are they?" section. It tells Claude how to frame the client's work and what they believe in.
What Claude does with it: Uses it to set tone and make sure copy reflects the client's stated values, not generic marketing-speak.
Common gap: Mission statements that are vague ("We help businesses grow"). Push clients to give you something specific that actually sounds like them.
What the client wants to write about, with context on why, and what topics to avoid completely.
What Claude does with it: Filters out topics that would get you in trouble and makes sure content stays on-brand.
Common gap: Avoid-lists that are too vague ("avoid political topics") rather than specific ("never reference specific party names, election results, or legislative positions").
What the client calls their audience, how they describe customer pain points, and how (or whether) they mention competitors.
What Claude does with it: Writes audience-appropriate copy and avoids language that would confuse or alienate the actual customers.
Common gap: Missing instructions about competitors. "Don't name competitors" is very different from "reference competitor pain points but never use their names."
This is the most important section for Claude. Capitalization rules, preferred phrases, hashtags, CTAs, promises to avoid, and the client-specific banned words list.
What Claude does with it: Applies specific language rules to every piece of copy in the project. This is where the voice gets specific.
Common gap: Not including a banned words list or specific grammar preferences. "They prefer sentence case in headlines" matters. So does "They always hyphenate 'co-pay.'"
Brand colors, fonts, photography style guidelines. Less directly used by Claude for text content, but helpful for the Design team and for prompts that need to describe the brand visually.
What Claude does with it: Uses it when asked to write alt text, image descriptions, or prompts for Ideogram.
The update workflow (for real this time)
We've said it a few times in this course already, but this is worth its own section because it's one of the most common gaps in how we use Claude.
- After every client check-in where feedback comes in, ask: "Does this change how Claude should write for this client?"
- If yes, update the Communication Codex in Google Drive.
- Export the updated document as a .TXT file.
- Open the client's Claude Project. Remove the old Codex file. Upload the new one.
- Post in Slack (#ai-and-automations or the client channel): "Updated [Client] Codex in Claude Project — added [what changed]." This keeps the whole team informed.
⚠️ Quarterly reminder: At the start of each quarter, review all your active Claude Projects and ask: "Is the Codex in here current?" Clients change. Their priorities shift. Language goes stale. A Codex that hasn't been touched in six months is probably inaccurate in at least a few ways.
OO's own Communication Codex
Online Optimism has a Communication Codex too. It's used for internal content like blog posts, social media, proposals, and agency marketing. The voice standards in this training course are drawn directly from it.
The OO Codex is what tells Claude to avoid the banned words list, use "Optimists" instead of "employees," never use em dashes, and write in a conversational tone that sounds like a smart coworker over coffee. If you're ever writing content for OO's own channels, start with our Claude Project, not a blank conversation.
Try it yourself
Open the Communication Codex Primary Template and read through it. Then find the Codex for one of the clients you work with and compare it to the template.
- What section is least complete in your client's Codex?
- Is there a banned words list? If not, what 3 to 5 words should be on it based on what you know about this client?
- When was the Codex last updated? Does it still reflect how the client talks about themselves?
Common Codex mistakes
- Keeping the Codex in PDF format. Always export and upload as .TXT. Claude reads PDFs poorly.
- Treating the Codex as a "set it and forget it" document. It should be updated any time the client gives feedback that changes how we write for them.
- Writing a Codex with vague language notes. "Professional tone" is not useful. "Never use contractions, always write in third person, avoid humor" is useful.
- Not uploading the Codex to the Claude Project at all. A Codex that lives only in Google Drive isn't helping Claude. Upload it.