Ubiquitous Language

Ubiquitous Language

> Upstream: Adapted from mattpocock/skills/ubiquitous-language. Concept from Eric Evans, Domain-Driven Design.

Extract and formalize domain terminology from the current conversation into a consistent glossary stored at product-docs/UBIQUITOUS_LANGUAGE.md. The same vocabulary is used by domain experts, the user, and the AI — both in planning docs (PRD, JTBD, discovery, tech-decomposition) and in code.

When this fires

• /nf Step 0: load existing glossary so discovery questions and the discovery doc use canonical terms.
• /nf Step 4 → Step 5 transition: after the grill round, update glossary with new terms before writing the discovery doc.
• /product Step 0 and after Step 4 grill: same pattern — load before interview, update before writing PRD/JTBD.
• /ct GATE 1: load alongside discovery/PRD docs so decomposition aligns with project terms.
• Manual invocation: any time the user asks to harden terminology or names a term that needs disambiguation.

Process

1. Read existing glossary at product-docs/UBIQUITOUS_LANGUAGE.md (if it exists). Hold its content in memory — do NOT use Edit/section-patching. The file is small; the safe path is read → merge in memory → overwrite.
2. Scan the relevant scope for domain-relevant nouns, verbs, and concepts:

• Current conversation
• The active task's PRD / JTBD / discovery doc
• Source code only when terms are ambiguous and the code resolves them

1. Identify problems:

• Same word used for different concepts (ambiguity)
• Different words used for the same concept (synonyms)
• Vague or overloaded terms

1. Merge in memory: combine existing entries with new findings. Preserve every existing term unless evidence shows it's wrong; revise definitions that have sharpened. Add newly discovered terms. Update "Flagged ambiguities" with anything resolved.
2. Ensure parent directory exists before writing: mkdir -p product-docs/ (the directory is repo-level, alongside .claude/, and may not exist on a fresh repo).
3. Write the full merged glossary to product-docs/UBIQUITOUS_LANGUAGE.md, fully overwriting the prior file.
4. Output a summary inline so the caller (/nf, /product, /ct) can paste it into its doc.

Output format

product-docs/UBIQUITOUS_LANGUAGE.md:

# Ubiquitous Language

> Domain terms used across PRDs, JTBDs, discovery docs, tech-decompositions, and code. Update via the `/ubiquitous-language` skill — auto-invoked from `/nf`, `/product`, `/ct`.

## [Subdomain or lifecycle name]

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

## Example dialogue

> **Dev:** "When a **Customer** places an **Order**, do we create the **Invoice** immediately?"
> **Domain expert:** "No — an **Invoice** is only generated once a **Fulfillment** is confirmed."

## Flagged ambiguities

- "account" was used to mean both **Customer** and **User** — these are distinct: a **Customer** places orders, while a **User** is an authentication identity.

Rules

• Be opinionated. When multiple words exist for the same concept, pick one and list the others as aliases to avoid.
• Flag conflicts explicitly. If a term is used ambiguously, call it out in "Flagged ambiguities" with a recommendation.
• Only domain terms. Skip generic programming concepts (array, function, endpoint) and skip the names of modules or classes unless they have meaning in the domain language.
• Tight definitions. One sentence max. Define what it IS, not what it does.
• Show relationships. Use bold term names; express cardinality where obvious.
• Group into multiple tables when natural clusters emerge (subdomain, lifecycle, actor). One table is fine if the domain is cohesive.
• Write an example dialogue. A short conversation (3-5 exchanges) between a dev and a domain expert that uses the terms precisely. The dialogue clarifies boundaries between related concepts.
• No file paths or code snippets. This is a domain document, not an implementation reference.

Re-running

When invoked again in the same conversation:

1. Read existing UBIQUITOUS_LANGUAGE.md
2. Incorporate new terms from subsequent discussion
3. Update definitions if understanding has evolved
4. Re-flag any new ambiguities
5. Rewrite the example dialogue to incorporate new terms

Return to caller

After writing/updating the file, return a compact summary so /nf, /product, or /ct can reference it without re-reading the file:

• Terms added: [list]
• Terms revised: [list]
• Ambiguities flagged: [list]
• Suggested canonical phrasing for the upcoming doc: [1-3 examples]

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: alexandrbasis
• Source: alexandrbasis/claudops
• License: MIT

Install and usage instructions live in the source repository linked above.