--- title: "Check the master list before you add a new value - Atlan MCP Cookbook" url: "https://atlan.com/mcp-cookbook/check-value-against-master-list/" description: "Before adding a new value to a field, pull the existing values so a new entry doesn't duplicate one under a different name and fragment the master list." --- > Atlan is hosting Context Conference, bringing together the leaders and builders at the frontier of giving AI the context it needs to understand their business. It runs online on October 28, 2026, from 11:00 AM to 2:00 PM ET. Atlan co-founder Prukalpa Sankar opens and closes the day. Leaders from AstraZeneca, BNY and Verizon share why they invest in context and what they get from it. Registrants get early access to The AI Context Gap, a new study from MIT Technology Review Insights. Register: https://atlan.com/context-conference/ Recipe 28 in [The Atlan MCP Cookbook](https://atlan.com/mcp-cookbook/). Before adding a new value to a field, pull the existing values so a new entry doesn't duplicate one under a different name and fragment the master list. Use case: Govern & keep trusted / Action: Look up / Persona: Data/Business User, Data/BI Analyst, Data Governance Lead / Effort: Quick / Runs in: any AI tool Requires Atlan MCP connected to your AI tool: [set up Atlan MCP](https://docs.atlan.com/product/capabilities/atlan-ai/how-tos/remote-mcp-overview). ## 1. The task **Scenario.** Someone's about to add a new category to a field, say a new `product_category` value, but the field already has a governed set of values. If the new one duplicates an existing value under a slightly different name, "Eco" vs "Eco-Friendly" vs "Green", it fragments the master list and quietly breaks every report that groups by it. Before adding, they check what's already there. The ask: - The current set of distinct values already on the field - Whether the value you're about to add already exists under another name - A clear reuse-or-add decision, instead of a silent duplicate Hero prompt: "Before I add `Eco-Friendly` to `product_category`, show me the existing distinct values so I can tell if it already exists under another name." Step by step: 1. Pull the current value set. Prompt: "List the existing distinct values in [product_category], so I can see the master list I'd be adding to." 2. Check the proposed value against it. Prompt: "Does [Eco-Friendly] already exist in that list, exactly or as a near-variant like [Eco] or [Green]? Flag the closest matches." 3. Decide: reuse or add. Prompt: "Recommend whether to reuse an existing value or add a genuinely new one, and if new, whether [Eco-Friendly] fits the naming pattern of the rest." ## 2. What you'll give it Required context: - The field you're adding a value to - The value you're proposing to add - Read access to the connected source through Atlan, with query permission Optional context: - The naming convention for the field, if one exists, so a new value can be checked against it - Any governed term or documentation that defines the allowed set ## 3. What Atlan creates Outputs: - The current distinct values in the field, the effective master list - The closest existing matches to your proposed value, exact or near-variant - A reuse-or-add recommendation, with a naming-fit check if it's genuinely new **Summary.** You add a value that fits the governed set instead of a near-duplicate that fragments it, so reports that group by the field keep reconciling. **Read-only.** Read-only in Atlan. It checks the existing values so you can decide; the value itself is added in the source system, not here. ## 4. Follow-up prompts - **Check the whole load:** "Run this check across every field I'm about to add values to in this load, not just one." - **Find near-duplicates:** "Show me values that already look like near-duplicates of each other, so I can flag the mess that's already there." - **Define it properly:** "If we add it, draft a one-line definition so the next person knows when to use it." ## 5. Tips & troubleshooting **Cook's note.** The expensive mistake isn't a typo, it's a synonym. "Eco" and "Eco-Friendly" both look fine until a report splits one category into two. - Match the client to the work.** Use a client that shows the full existing value list, so you're judging against everything, not just the top few. - Automate or chain it.** Run this ahead of any bulk load that introduces new category values, so variants get caught before they land, not after. - Ask what it found.** Have it list the near-variants it matched against, so the reuse-or-add call is on the record. ## Related recipes - [Profile a field's shape before you build on it](https://atlan.com/mcp-cookbook/profile-a-field-before-you-build-on-it/): Get a quick profile of a field, its type, null rate, distinct count, and range, so you know what you're working with before you aggregate or join on it. - [Give one concept one trusted definition](https://atlan.com/mcp-cookbook/reconcile-terminology-across-systems/): Confirm whether two differently-named fields or terms mean the same thing, then link them under one governed definition so the next person searching either name lands in the same place. - [Grow your business glossary](https://atlan.com/mcp-cookbook/grow-your-business-glossary/): Bootstrap glossary terms from how your assets already use business concepts. [Browse all recipes](https://atlan.com/mcp-cookbook/) / [Set up Atlan MCP](https://docs.atlan.com/product/capabilities/atlan-ai/how-tos/remote-mcp-overview)