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Build a Custom-Resume Gem in Gemini

This is the system I use to tailor a resume to any job in a few minutes, in my own voice and grounded in my real experience. Build it once, reuse it every time you apply. It works in any modern AI tool, not just Gemini.

Download as MarkdownSee the portfolio-site walkthrough

Build a Custom-Resume Gem in Google Gemini

This is the exact system I use to tailor a resume to any job in a few minutes, in my own voice, grounded in my real experience. You build it once, then reuse it every time you apply.

It works in any modern AI tool. I use a Gemini Gem because it is free and the files stay attached. The same four files work just as well as a Claude Project.

The whole idea: stop pasting a resume and a job description into a chatbot and hoping. Give the AI real context about you, once, and it stops guessing.

What you build first: four files

These four files are the system. Spend your time here. Everything downstream gets better when these are good.

  1. Master Resume. Everything you have done, long form. Career narrative, quantified results by role, technical skills, certifications, operating style, target environment. Over-include now. You will trim per application later.
  2. Voice and Style Guide. How you actually write. Sentence structure, formatting preferences, openers, closers, and a "Never Use" list. This is what removes the AI tell.
  3. Ground Rules. What the AI must always do, must never do, and a quality checklist to run before it hands you anything.
  4. Personal Highlights. The human details. Where you live, what energizes you, community involvement, professional networks, recent learning, how colleagues describe you.

Write them in a Google Doc, then download as Markdown (File, Download, Markdown). AI tools read and write Markdown far better than a PDF.

Build the four files: let the AI interview you

You do not write these from a blank page. You let the AI interview you, one question at a time, then have it compile your answers into a clean file. Each one takes 15 to 30 minutes. Do them in separate chats.

If your AI already knows you well from months of use, you can shortcut this: paste your resume and say "fill this out based on what you know about me," then correct it. If not, the interview gets you there.

File 1: Master Resume

Start a new chat and paste:

I need your help building a comprehensive career master document. This will be the single source of truth that AI tools use to generate tailored resumes. It needs to be specific, metric-driven, and grounded in real examples.

Interview me on these topics, one at a time. Push me for numbers, names, and specifics. Don't accept vague answers.

1. Career narrative: what's the arc? What connects my roles? What's the core problem I solve?
2. Quantified results from each role: revenue managed, retention rates, growth percentages, team sizes, deal sizes, customer counts. Real numbers.
3. Technical skills and certifications: what I actually know versus what I've just seen on a slide.
4. A specific example of handling a crisis or delivering bad news to a customer or stakeholder.
5. Industries and company types I've worked in (size, stage, vertical).
6. Target environment and ideal next role.

Start with topic 1. Don't let me off the hook with generalities.

When the interview is done, paste:

Compile everything into a single Master Resume document with these sections:
1. Career Narrative
2. Quantified Results and Achievements (organized by company and role)
3. Technical Skills and Certifications
4. Operational Style and Crisis Management
5. Target Environment and Next Role

Use bullet points. Lead with the metric or fact, then the context. No filler.

File 2: Voice and Style Guide

In a new chat, paste:

I need to build a personal voice and style guide for AI writing tools. This guide will ensure that anything AI writes on my behalf sounds like me, not a generic corporate robot.

Interview me on these topics, one at a time. Push me for specifics.

1. How I naturally communicate (direct, warm, formal, casual).
2. How I structure my thinking when I write (do I lead with the ask, build context first).
3. Words and phrases I actually use in professional writing.
4. Words, phrases, and patterns I hate seeing in AI output.
5. How I open and close emails.
6. Formatting preferences (bullets, paragraphs, headers).

Start with topic 1.

When the AI asks for examples, paste in a real email you wrote. Then compile:

Compile everything into a Voice and Style Guide with two sections.

Section 1, "How I Write": my communication style, structure, vocabulary, openers, closers, and formatting preferences.

Section 2, "Never Use List": every word, phrase, pattern, and structural habit I said I don't want AI to use. Be exhaustive. If I said I hate it, it goes on this list.

End the document with a paste-ready system prompt I can copy into any AI tool.

File 3: Ground Rules

In a new chat, paste:

I need to build a ground rules file for an AI resume assistant. These are behavioral instructions the AI must follow every time it writes on my behalf.

Interview me on these topics, one at a time:

1. What should the AI always do before starting to write (read all files, confirm the target role).
2. What rules must it follow during writing (only use facts from my files, never invent experience).
3. What output format do I want (one page, bullet points, specific section order).
4. What should it never do (fabricate metrics, add skills I don't have, use certain formatting).
5. What quality checks should it run before calling a resume done.

Start with topic 1.

Then compile:

Compile everything into a Ground Rules document with three sections:

Section 1, "Always Do": things the AI must do before starting and during writing.
Section 2, "Never Do": banned behaviors, formatting, and content.
Section 3, "Quality Check": a checklist the AI runs before finalizing any resume.

Write everything as direct instructions. Not suggestions. Rules.

File 4: Personal Highlights

In a new chat, paste:

I need to build a personal highlights file for AI writing tools. These are the human details that make my applications feel personal, not generic.

Interview me on these topics, one at a time:

1. Location, work preferences (remote, hybrid, onsite), timezone.
2. What energizes me at work (not what I'm good at, what I actually enjoy).
3. Community involvement (volunteering, coaching, boards, local organizations).
4. Professional networks and groups I actively participate in.
5. Recent learning (certifications, courses, self-directed projects).
6. How a former colleague, manager, or direct report would describe working with me.
7. Something distinctive about my background that doesn't fit a standard resume but makes me memorable.

Start with topic 1.

Then compile:

Compile everything into a Personal Highlights document with these sections:
1. Location and Preferences
2. What Energizes Me
3. Community Involvement
4. Professional Networks and Groups
5. Recent Learning
6. How Colleagues Describe Me
7. The Distinctive Detail

Keep it concise. This is the shortest of the four files.

When all four are done, download each as Markdown (File, Download, Markdown). Now you build the Gem.

Build the Gem

Step 1: Open Gem Manager

Go to gemini.google.com. In the left sidebar, open Gem Manager, then click New Gem.

Step 2: Name it

Something like "My Resume Builder." This is only for your own organization.

Step 3: Upload your four files to Knowledge

Before you paste any instructions, upload the four files into the Gem's Knowledge. These become its permanent reference material.

Step 4: Add the instructions

Paste this into the Instructions box:

You are a custom AI assistant built to write and edit my career documents (resumes, cover letters, LinkedIn content, and interview prep).

You have four files in your Knowledge. Use them as follows:

MASTER RESUME FILE (your primary source of truth):
- This file contains my career narrative, quantified results by role, technical skills, certifications, operational style, and target environment.
- Build all content strictly from this file. Do not invent experience, metrics, companies, or skills that are not in this file.
- Every claim must be grounded in a specific number, example, or outcome from this file.
- Default to bullet points. Lead with the metric or result, then the context.

VOICE AND STYLE GUIDE FILE (how to write):
- This file contains my communication style, sentence structure, formatting preferences, openers, closers, and a "Never Use" list.
- Write everything following the rules in this file.
- Pay close attention to the "Never Use" list. If a word, phrase, or pattern appears on that list, do not use it under any circumstances.
- The reader should hear me saying it. If it sounds like a generic AI wrote it, rewrite it.

GROUND RULES FILE (behavioral instructions):
- This file contains rules the AI must follow: what to always do, what to never do, and a quality checklist.
- Follow all "Always Do" and "Never Do" rules without exception.
- Before finalizing any document, run the Quality Check at the bottom of this file. If any item fails, fix it before presenting the output.

PERSONAL HIGHLIGHTS FILE (the human details):
- This file contains personal context that makes applications feel human: location, what energizes me, community involvement, professional networks, recent learning, how colleagues describe me, and distinctive details.
- Use this file for cover letters, professional summaries, and any content that benefits from personality and context beyond raw career metrics.
- Draw from this file to make output feel like a real person, not a template.

OUTPUT FORMAT:
- Clean, scannable layout
- Bold headers where needed
- Bullet points for experience sections
- No excessive formatting or decoration
- Match the formatting preferences described in the Voice and Style Guide file

Step 5: Save

Click Create. Your Gem is now in your Gem Manager, ready to use.

Use the Gem

Tailor a resume to a job

Open the Gem and paste:

Review the following job description and tailor my resume to align with it.

Pull all career content from my Master Resume file in your Knowledge.
Write following the rules in my Voice and Style Guide file in your Knowledge.
Follow all instructions in my Ground Rules file. Run the Quality Check before finalizing.
Use my Personal Highlights where they add value to the application.
Do not invent experience or deviate from my style rules.

[PASTE THE FULL JOB DESCRIPTION HERE]

Add quick company research

Two minutes of research makes the output sharper. Ask any AI "What does [company] do, what do they sell, and who do they sell to?" then include it:

I'm applying for [ROLE TITLE] at [COMPANY NAME].

Here's the job description:
[PASTE JOB DESCRIPTION]

Here's my research on the company:
[PASTE COMPANY RESEARCH]

Tailor my resume to this role. Align my experience with the specific problems this company solves. Pull all career content from my Master Resume file. Write in my voice using my Voice and Style Guide file. Follow all Ground Rules and run the Quality Check before finalizing. Use my Personal Highlights where they add value.

Write a matching cover letter

Write a cover letter for this role. Keep it to one page. Lead with what I bring to the specific problem this company is solving.

Use my Voice and Style Guide file for tone, openers, and closers.
Pull substance from my Master Resume file.
Draw personal context from my Personal Highlights file.
Follow all Ground Rules.

[PASTE JOB DESCRIPTION]

Fix anything that is off

Talk to it like an assistant. Be specific:

  • "The second bullet is too generic. Use my specific NRR number from my Master Resume file."
  • "You used an em dash in paragraph three. Check my Never Use list."
  • "This sounds too formal. Match the email voice in my Voice and Style Guide."
  • "This resume doesn't mention my FinOps experience. Add it from my Master Resume."

Review every resume before you send it

  1. Metrics. Every number comes from your Master Resume, not invented.
  2. Experience. Nothing fabricated. If you do not have it, it is not on the resume.
  3. Voice. Read it out loud. Does it sound like you?
  4. Rules. No banned words or patterns from your Never Use list.
  5. Fit. It speaks the company's language and maps to the specific role.

Then do the final formatting in a Word doc. The AI gets you most of the way. You trim the oldest roles to land it on two pages and ship it.

Keep it current

Your Gem uses whatever files are in its Knowledge right now, so re-upload when you make changes.

  • Update the Master Resume when you finish a project, hit a new metric, or change your target role.
  • Update the Voice and Style Guide when you catch the AI doing something you do not like. Add it to the Never Use list.
  • Update the Ground Rules when you find a new behavior to enforce or ban.
  • Update the Personal Highlights when you join a community, earn a certification, or have a new story worth telling.

Built by Nathan Spear. Questions, or want the blank templates? Reach me through nathanspear.com.