Phase 4 · Gemini · Level 2 · Practitioner
Gems: your reusable Gemini experts
By the end, you'll be able to…
- Build a custom Gem with a clear role, instructions and output format
- Anchor a Gem to specific Drive files so it always answers from your material
- Choose a premade Gem from the gallery and know when to build your own instead
Why it matters
A Gem is a saved version of Gemini with your instructions and your files already baked in, so you stop re-explaining the same context every time. Once you've built one good Gem for a recurring task, you get consistent, on-brief answers with a single click. This lesson builds a real Fernway Gem you could use every week and shows how to anchor it to your own documents.
What a Gem actually is
A Gem is a custom version of Gemini you set up once and reuse. Instead of typing the same role and instructions into a fresh prompt every time ("you're a sales assistant, our products are these, keep replies under 100 words, British spelling"), you save all of that into a Gem, give it a name, and from then on you just ask your question. The Gem remembers who it's meant to be.
Two things make Gems more than a saved prompt. First, you can attach files as knowledge, so the Gem answers from your material rather than the model's general training. Second, if those files live in Google Drive, the Gem uses the latest version each time. Update the file and the Gem is up to date automatically. Google's own tips for creating custom Gems is the reference page.
Gems are available in the free Gemini app, so anyone with a Google account can build one. The knowledge-file feature (attaching your own documents, especially from Drive) is the part most likely to depend on your account and plan, and connecting Drive requires the relevant Google account settings switched on. As always, if a button is missing it's an account matter, not a fault. We'll build a Gem for Fernway, where you're Tom Elliott and you answer the same kind of sales questions every week.
Building a Gem, part by part
In the Gemini app, open Explore Gems (or Gem manager) and choose New Gem. You'll fill in a few things:
- Name. What it's called in your list, e.g. "Fernway Sales Assistant".
- Instructions. The heart of the Gem: who it is, what it does, the tone, the format, and what it must not do. This is a prompt you write once and reuse forever, so it's worth spending five minutes on.
- Knowledge. Files that give the Gem its context (more on this below).
The instructions are where the quality lives. Vague instructions give a vague Gem; the role, task, context and format habit from Phase 0 applies directly. Here's a solid starting set for Tom's Gem.
You are the sales assistant for Fernway, a UK company. Our products are the Starter Plan (£49), the Pro Plan (£120) and the Add-on Pack (£15). Always use British spelling and a warm, plain, non-pushy tone. When I ask for an email, keep it under 120 words unless I say otherwise, and end with one clear next step. When I ask about our sales figures or accounts, only use the files I've given you. If the answer isn't in them, say so rather than guessing, and tell me which file you'd need. Never invent numbers, dates or customer names.
Why this works: Setting the role, the house rules, the format and an explicit honesty instruction ('say so rather than guess') turns a blank assistant into a consistent, on-brief one, and the 'don't invent' line guards against confident fabrication every time you use it.
Save that, and every future chat with this Gem starts with all of it already in force. You've turned a paragraph you'd otherwise retype daily into a one-click expert.
Anchoring a Gem to specific Drive files
Instructions shape how a Gem behaves; knowledge files decide what it knows. In the Knowledge section you can attach files, including choosing them straight from Google Drive. Google currently caps this at around ten files, and the durable rule is what matters: a Gem anchored to your files answers from those files first.
The Drive advantage is worth stressing. When you attach a Drive file, the Gem reads the current version each time you use it. So if Tom anchors his Gem to a living "Fernway sales figures" sheet, he updates the sheet once a week and the Gem's answers stay current with no re-uploading. Attach the sales spreadsheet, the remote-working policy and the project brief, and the Gem becomes a genuine Fernway expert.
Once anchored, you ask questions and the Gem grounds its answers in those documents. This is grounding again, made permanent.
Which region had the weakest sales last month, and does our remote-working policy affect how that team is staffed? Answer from my attached files only, cite which file each point comes from, and flag anything the files don't actually tell you.
Why this works: Because the Gem already holds the files and the honesty instruction, you can ask a direct business question without re-pasting anything, and asking it to cite the source file keeps you able to verify, which the 'say so rather than guess' instruction reinforces.
If the answer cites the sales sheet for the figure and the policy doc for the staffing point, and openly says where the files fall silent, the Gem is doing exactly what you built it for.
The premade Gem gallery
You don't have to build from scratch. Gemini ships a gallery of premade Gems (things like a brainstorming partner, a writing editor, a coding helper or a career coach) that you can use immediately from Explore Gems. They're a fast way to see what a well-written Gem feels like, and a good starting point you can copy and adapt. Reach for a premade Gem when your need is generic (brainstorming, tidying prose); build your own when the value is in your context, your products, your files, your house style, which no premade Gem can know. The two prompt cards below show custom Gems worth building.
Example prompts
You turn messy meeting notes into a clean summary. Always output: (1) a three-sentence overview, (2) a decisions list, (3) an actions table with columns Action, Owner, Due date. Mark any action with no owner as UNASSIGNED. Only use what's in the notes I paste. Don't invent owners or dates.
Why this works: A single-job Gem with a fixed output shape gives you identical, scannable notes every time. The consistency is the point, and pre-deciding the format means you never re-specify it.
You answer staff questions about Fernway's remote-working policy, using only the attached policy document. Quote the relevant part, then explain it in plain English. If the policy doesn't cover the question, say so clearly and suggest who to ask. Don't guess the rule.
Why this works: Anchoring a Gem to a policy document and forbidding it from answering beyond the file makes it a safe internal helper: it can only tell people what the policy actually says, not what it assumes.
I'm adapting the premade writing-editor Gem for Fernway. Add these rules: British spelling, warm but concise tone, always keep customer emails under 120 words, and never change any figures or dates in what I paste. Rewrite the instructions to include these.
Why this works: Starting from a premade Gem and layering your specifics on top is faster than a blank page, so you keep a proven structure and add only the context that makes it yours.
Try it now
Common mistakes
- Thin instructions. "You help with sales" produces a generic assistant. Spell out the products, the tone, the format and the limits; the Gem is only as good as the brief you give it once.
- Forgetting the honesty rule. Without an explicit "say so rather than guess" instruction, an anchored Gem will still try to answer questions your files don't cover, and it'll sound just as confident when it's making it up.
- Assuming anchored means accurate. A Gem answers from your files, but it can still misread them. Keep asking for the source file and spot-check, exactly as you would with any Gemini answer.
- Attaching stale files. A Gem anchored to an out-of-date sheet gives out-of-date answers with full confidence. Anchor to a living Drive file where you can, and remember the Gem is only as current as its documents.
- Building a Gem for a one-off. Gems earn their keep on recurring tasks. For a single job, a good one-off prompt is quicker than setting up and maintaining a Gem.
Keeping current
Gems, the knowledge-file limits and the premade gallery all change as Google develops them. When your screen differs from this lesson, trust it and check Google's official pages: Use Gems in Gemini Apps and Use Gems with Gemini in Google Drive. Accurate as of 13 July 2026.