Ubiquitous Language

Ubiquitous Language

Define the domain model's vocabulary. Each term in this glossary is a model element — changing a term here means changing the model and the code.

Invocation Position

This is a side-route skill that sharpens shared language across the rest of the workflow.

Use /ubiquitous-language when terminology is fuzzy, stakeholders are using conflicting terms, or you want a glossary that improves shaping, QA, issue writing, and refactor conversations.

Do not use it as a substitute for feature shaping or implementation. Its job is to improve the language of those workflows, not replace them.

One question per turn. When walking a workflow story or proposing canonical terms, ask one question at a time and wait for the user's answer before asking the next. Language work is a conversation, not a questionnaire.

Prefer single-select. Use single-select multiple choice when the user is choosing one direction, one priority, or one next step.

Use multi-select rarely. Reserve it for compatible sets — goals, constraints, non-goals, success criteria — that can all coexist. If prioritization matters, follow up asking which selected item is primary.

Use the platform's question tool when available. In Claude Code, use AskUserQuestion; in Codex, request_user_input; in Gemini, ask_user. Otherwise, present numbered options in chat and wait for the user's reply before proceeding.

Process

1. Walk one workflow as a story before extracting terms. Ask for one concrete story in the form "[who] does [what] using [tool]." Treat the nouns in the story as term candidates and the verbs as behavior candidates.
2. Scan the conversation for domain-relevant nouns, verbs, and concepts. Pay special attention when a domain expert corrects a developer's word choice — these corrections are high-value signals.
3. Surface implicit concepts — look for domain knowledge that is discussed but never named:
   • Circumlocutions: a concept explained in a full clause because no term exists yet
   • Hidden rules: conditional logic or eligibility checks described procedurally ("if X and Y and Z...") that could be named as a policy or constraint
   • Contradictions: apparent disagreements between participants that would dissolve if a new concept were introduced
4. Identify problems:
   • Same word used for different concepts (ambiguity)
   • Different words used for the same concept (synonyms)
   • Vague or overloaded terms
5. Propose a canonical glossary with opinionated term choices
6. Check model-code correspondence (when a codebase is present). Scan class, module, and function names for terms that diverge from the glossary. Record divergences as model-code fractures.
7. Write to UBIQUITOUS_LANGUAGE.md in the working directory using the format below
8. Output a summary inline in the conversation

Output Format

Write a UBIQUITOUS_LANGUAGE.md file with this structure:

# Ubiquitous Language

## Order lifecycle

| Term        | Definition                                              | Aliases to avoid      |
| ----------- | ------------------------------------------------------- | --------------------- |
| **Order**   | A customer's request to purchase one or more items      | Purchase, transaction |
| **Invoice** | A request for payment sent to a customer after delivery | Bill, payment request |

## People

| Term         | Definition                                  | Aliases to avoid       |
| ------------ | ------------------------------------------- | ---------------------- |
| **Customer** | A person or organization that places orders | Client, buyer, account |
| **User**     | An authentication identity in the system    | Login, account         |

## Relationships

- An **Invoice** belongs to exactly one **Customer**
- An **Order** produces one or more **Invoices**

## Surfaced implicit concepts

| Proposed term       | Evidence                                                                                       |
| ------------------- | ---------------------------------------------------------------------------------------------- |
| **Shipping Policy** | Described procedurally three times ("if the total is above $50 and...") but never given a name |

## Flagged ambiguities

- "account" was used to mean both **Customer** and **User** — these are distinct concepts: a **Customer** places orders, while a **User** is an authentication identity that may or may not represent a **Customer**.

## Model-code fractures

_Include only when a codebase was scanned._

| Glossary term   | Code identifier    | Location                        | Recommendation          |
| --------------- | ------------------ | ------------------------------- | ----------------------- |
| **Fulfillment** | `order_processing` | `src/services/order_processing` | Rename to `fulfillment` |

Handoff

• Expected input: domain language ambiguity, competing terminology, or a need to harden vocabulary before downstream work
• Produces: UBIQUITOUS_LANGUAGE.md and clearer naming for issues, specs, QA, and refactor discussion
• Supports: /shape, /write-a-prd, /qa, /triage-issue, and refactor planning by giving those skills sharper domain terms
• What comes next: return to the workflow that needed better language, now using the glossary consistently

Rules

• This glossary is the model, not documentation of it. If a term is renamed or redefined here, treat it as a model change that should be reflected in code. If a term exists in code but not here, the glossary is incomplete.
• Be opinionated. When multiple words exist for the same concept, pick the best one and list the others as aliases to avoid.
• Flag conflicts explicitly. If a term is used ambiguously in the conversation, call it out in the "Flagged ambiguities" section with a clear recommendation. If the same word legitimately means different things in different subdomains, note it as cross-context divergence rather than a defect.
• Name the unnamed. When a concept appears only as clauses, conditionals, or procedural descriptions ("if X and Y and not Z..."), propose a canonical name for it (e.g., "Free Shipping Eligibility," "Booking Validity"). These are often the highest-value terms in the glossary.
• Only include domain terms. Skip generic programming concepts (array, function, endpoint) and module/class names unless they have meaning in the domain language.
• Keep definitions tight. One sentence max. Define what it IS, not what it does.
• Show relationships. Use bold term names and express cardinality where obvious.
• Group terms into multiple tables when natural clusters emerge (e.g. by subdomain, lifecycle, or actor). Each group gets its own heading and table. If all terms belong to a single cohesive domain, one table is fine — don't force groupings.
• Classify when modeling, not when aligning. If the conversation involves design decisions about identity or lifecycle, add a "Classification" column (Entity, Value Object, or Service). Omit it when the glossary is purely for shared vocabulary between stakeholders.
• Run a "Modeling Out Loud" diagnostic (do not write it to the file). Mentally construct a scenario walkthrough (3-5 exchanges) that forces key glossary terms to bear weight in realistic sentences. If a term feels awkward, requires a parenthetical gloss, or gets silently replaced by a different word, the concept it represents is suspect. Record any findings in Surfaced implicit concepts (for unnamed concepts) or Flagged ambiguities (for term problems) — the dialogue itself is scaffolding that doesn't belong in the output.

Re-running

When invoked again in the same conversation:

1. Read the existing UBIQUITOUS_LANGUAGE.md
2. Incorporate any new terms from subsequent discussion
3. Surface any newly implicit concepts from subsequent discussion
4. Update definitions if understanding has evolved — each change is a model change, not just a wording fix
5. Re-flag any new ambiguities
6. Re-run the Modeling Out Loud diagnostic with new terms — record findings in Surfaced implicit concepts and Flagged ambiguities