Build Your Own AI Assistant: Gemini Skills, Claude Skills, ChatGPT Plugins and Grok Skills (Custom GPTs Are Retiring)

Build one reusable "Weekly Meal Planner" assistant three ways (as a Gemini skill, a Claude Skill and a ChatGPT plugin), so you stop pasting the same setup prompt every week. And move any old GPT or Gem before it's retired.

Checked October 17, 2026. Researched and drafted with help from Grok Bot.

Quick answer

• A custom assistant is a saved set of instructions (plus files and sometimes tools) that you call by name, like /meal-planner.
• The names changed in 2026. ChatGPT's custom GPTs are retiring, replaced by plugins (made with Plugin Creator). Gemini's Gems become skills on personal accounts starting November 2026. Claude has Skills.
• Free works in places. Claude Skills work on all plans, including Free. Gemini skills work on personal Google accounts (18+).
• A Project isn't the same thing. A Project is a folder for one topic. A skill or plugin is a recipe you can use in any chat.
• Grok: make a Skill (describe it in chat and Grok's Skill Creator saves it), or use a Project with instructions and files.

Comparison table

Chatbot	What it's called	How you build it	How you use it	Files	Plan
Gemini	Skills (Gems become skills from Nov 2026)	Settings → Skills → Create manually	Type / then pick it	✓ supported files carry over from Gems	Personal accounts, 18+
Claude	Skills	Customize → Skills: ask Claude, or upload a ZIP	Claude uses it when relevant, or ask by name	✓ inside the skill	All plans incl. Free; code execution on
ChatGPT	Plugins (with skills inside)	Install Plugin Creator, then chat with @plugin-creator	@ your plugin	✓ (e.g. a template)	Create on Go, Plus, Pro (not Free)
Grok	Skills (built-in Skill Creator)	Describe it in chat, upload a file, or write one from scratch	grok.com, iOS, Android	✓ (upload a file)	Plan not stated by SpaceXSI
Grok	Projects (instructions + files)	grok.com → Projects	Open the Project	✓	Steps from third-party guides; not verified
Perplexity	Project instructions	Projects	Open the Project	✓	Free with limits

Which one should I use? The verdict

Quick questions

Are custom GPTs going away? Yes. OpenAI is retiring custom GPTs and recommends moving workflows to plugins. New GPTs can't be created on personal accounts (Free, Go, Plus or Pro).

What happens to my Gemini Gems? Starting November 2026, Gems go away on personal Google accounts. Google recreates them as skills automatically, along with supported files. Work accounts follow in 2027.

What's the difference between a skill and a Project? A Project is a folder with chats and files for one topic. A skill is a reusable recipe you can call in any chat.

Do I need to code? No. Every method here starts with a form or a chat. Claude's ZIP upload is optional and covered in a "For the curious" box.

Can I share my assistant? Gemini Gems could be shared, but Gemini skills can't be shared yet (Google says it's coming soon). ChatGPT plugins can be shared inside Business and Enterprise workspaces. Claude Skills can be shared only on Team and Enterprise plans.

Before you start: write the recipe once

Every tool needs the same thing: a clear recipe. Write it in a note first.

NAME: Weekly Meal Planner
WHAT IT DOES: Plans 5 weeknight dinners and a grocery list for my family.
WHEN TO USE IT: When I say "plan meals" or "meal plan".
ABOUT US: 2 adults, 2 kids (8 and 11). One kid won't eat mushrooms. Budget $120/week. 30 minutes max on weeknights. We have an air fryer and a slow cooker.
STEPS:
1. Ask what's already in the fridge (one question only).
2. Plan 5 dinners: 1 slow cooker, 1 air fryer, 1 vegetarian, 2 quick.
3. Reuse ingredients across meals to save money.
4. Make a grocery list grouped by store aisle, with rough prices.
FORMAT: Table (Day | Dinner | Time | Notes), then the list.
NEVER: Never suggest mushrooms. Never go over budget without saying so.

Tip: paste your rough idea into any chatbot and say Turn this into a clear assistant recipe in the format above. Ask me up to 5 questions first.

Step by step: Gemini skills

1. Open gemini.google.com (personal Google account, 18+).
2. Go to Settings → Skills → Create manually.
3. Give it a name (Meal Planner) and paste your recipe as its instructions.
4. Add files if it needs them (for example, a family recipe list).
5. Save.
6. In any chat, type /, pick Meal Planner, and say plan meals.

Good to know: some Gemini tools don't work inside skills: video, music, Canvas, Deep Research and Guided learning.

Moving from Gems: you don't need to do anything. From November 2026, Google recreates your Gems as skills automatically. Open Settings → Skills afterward and check each one.

Step by step: Claude Skills

1. Turn on code execution (Claude's settings; skills need it).
2. Go to Customize → Skills. You'll see built-in skills for Excel, Word, PowerPoint and PDF.
3. The easy way: in a chat, say:

Help me make a skill from this recipe. Ask me anything you need, then create the skill.
[paste recipe]

Creating a skill just by chatting (instead of uploading a file) is not verified on Claude's help pages. If Claude can't save it for you, use the ZIP method in the box below.

4. Turn the skill on in Customize → Skills.
5. In any chat: Plan meals for next week. Claude uses the skill when it's relevant.

---
name: weekly-meal-planner
description: Plans 5 weeknight dinners and a grocery list for my family. Use when I ask for a meal plan.
---
[paste your recipe here]

Step by step: ChatGPT plugins (Plugin Creator)

1. In ChatGPT, open Plugins in the sidebar.
2. Find Plugin Creator and install it. (Or select Add (+) in Plugins, which opens Plugin Creator.)
3. Start a chat with @plugin-creator and describe your assistant:

Create a "Weekly Meal Planner" plugin with one skill that follows this recipe exactly. It doesn't need to connect to any apps.
[paste recipe]

4. Work through its questions. Plugins with only skills install automatically and may not show an install card.
5. Use it: type @Weekly Meal Planner and plan meals.
6. To change it later: @plugin-creator Update Weekly Meal Planner to add a Sunday batch-cook.

Plugin Creator works on Plus (and Go and Pro), but not Free, per OpenAI's pricing page. On Free, use a ChatGPT Project with your recipe as its instructions.

Moving an old GPT: open your GPT, copy its instructions and files, and paste them into Plugin Creator (or a Project). New GPTs can't be created on personal accounts.

Step by step: Grok Skills (and Projects)

Grok Skills are on grok.com and the Grok iOS and Android apps. The built-in Skill Creator lets you describe a skill in conversation, upload a file, or write one from scratch.

Make a skill from this recipe. Ask me anything you need first.
[paste recipe]

Where Skill Creator sits in the menu, and which plans include Skills, aren't stated on SpaceXSI's announcement (not verified). If you can't find it, use a Project:

1. Go to grok.com in a standard Chrome browser and sign in. (SpaceXSI notes some web addresses are missing features like Projects.)
2. Create a Project and add your recipe as its instructions.
3. Add files if needed.
4. Start chats inside the Project. Use Expert for big planning jobs.

Not verified on an official page: Grok Project button names and limits (steps from third-party guides).

The others

Try it: 3 ready-made assistants

Small-business helper

NAME: Shop Helper
WHAT IT DOES: Writes customer replies, product descriptions and weekly promo ideas for [business].
ABOUT US: [what you sell, prices, tone, return policy, hours]
STEPS: Ask which job (reply / description / promo). For replies, keep under 120 words, warm and clear. For descriptions, 3 bullet benefits + 1 line of specs.
NEVER: Never promise refunds or discounts not in the policy. Never invent product details; ask me.

Homework coach

NAME: Homework Coach
WHAT IT DOES: Helps my [grade] kid understand homework without giving answers.
STEPS: Ask what the question is. Explain the idea with a simple example. Ask one question back. Give hints, not answers.
NEVER: Never give the final answer to graded work. Keep it friendly and short.

Email polisher

NAME: Email Polisher
WHAT IT DOES: Rewrites my drafts so they're clear, polite and short.
STEPS: Keep my meaning. Cut length by a third. Put the ask in the first two lines. Offer a subject line.
NEVER: Never add facts I didn't write.

Common mistakes and fixes

Mistake	Fix
Assistant ignores a rule	Move the rule to a NEVER line and make it specific
It asks too many questions	"Ask at most one question, then go"
It's too long	Add a format line with a length limit
Gemini skill can't use Canvas or Deep Research	Those tools aren't supported in skills; use a normal chat
Claude skill never triggers	Make the description say exactly when to use it
Can't create a ChatGPT plugin	Use a Project with the recipe as instructions

Prompt pack

Recipe writer:

I want a reusable assistant for [job]. Interview me (max 5 questions), then write the recipe with NAME, WHAT IT DOES, WHEN TO USE IT, ABOUT ME, STEPS, FORMAT, NEVER.

Recipe tester:

Pretend you are this assistant: [paste recipe]. Here are 3 test requests: [1], [2], [3]. Answer each. Then tell me which rules were unclear or conflicting.

GPT/Gem mover:

Here are my old GPT's instructions: [paste]. Rewrite them as a clear skill recipe in the format above, removing anything that only made sense in GPTs.

Next level

Make your assistant run on its own: A4: Put AI on Autopilot shows scheduled and email-triggered automations in Grok, ChatGPT, Claude and Gemini.