Home › Skills vs custom instructions

Gemini Skills vs custom instructions: which one do you need?

Gemini gives you at least three ways to change how it responds: custom instructions, Gems, and Skills. They are not competing versions of the same feature — they apply at different scopes. Custom instructions shape every conversation you have. Skills sit dormant until a request matches them. Choosing the wrong one is a common reason people build something that never fires.

Quick decision:

Custom instructions for things that should always be true — your role, your tone, your formatting preferences. Applied to every conversation, no trigger needed.
Skills for things that apply only sometimes — a specific format, a specific workflow, a specific file type. They trigger when the request matches the description.
Gems for things you open deliberately, and they disappear on November 17, 2026.

Scope is the whole difference

Aspect	Custom instructions	Skills	Gems
When it applies	Every conversation, always	Only when the request matches the description	When you open it
Trigger required	No	Yes, and this is where most skills fail	You choose
How many you can have	One set	Up to 100 active, 100 MB total	No published limit
Can include files	No, text only	Yes, reference files travel with it	Uploaded files, partially
Per-project	No	No, skills are account-level	No
After Nov 17, 2026	Unaffected	Unaffected	Gone

Note on per-project behaviour: none of the three is scoped to a single project directory. Skills are account-level, which means two projects with contradictory conventions can produce unpredictable results. If you work across projects with very different conventions, keeping instructions outside the account is safer.

Where custom instructions win

Custom instructions are for facts that are true in every conversation:

Who you are and what you do
The tone you want back
Units, date format, currency
Standing constraints like "never use emoji" or "always show the calculation"
What you are working on, stated once

Anything here does not need a trigger because there is no trigger — it is always on. That makes it the cheapest possible place to put a preference.

Limits worth knowing

Custom instructions occupy space in every request. Google has tightened how much fits, and the practical effect is that long lists get dropped or ignored without warning. If your instructions are long enough that you are not sure everything fits, the fix is to move the situational parts into skills.

Instruction type	Where it belongs
"Always answer in British English"	Custom instructions
"I am a CNC programmer"	Custom instructions
"Use this exact template when writing change requests"	Skill
"When I paste a PDF, extract the tables into CSV"	Skill
"Prefer metric units"	Custom instructions
"For this client's reports, use their logo and colours"	Skill

Where skills win

A skill is worth building when the behaviour is conditional. Four signals that you need one:

You keep re-explaining it. If you have typed the same instruction into a chat three times, that instruction is a skill.
It only makes sense in one context. "Write in our house style" is meaningless outside that context, so it does not belong in always-on instructions.
It needs files. Templates, examples, reference documents. Custom instructions cannot carry those.
You would want it gone sometimes. Always-on instructions cannot be switched off. Skills can.

The most common mistake: putting a conditional workflow into custom instructions and then being annoyed that Gemini applies it when it should not. A skill that stays silent until it is relevant is strictly better than an always-on rule you have to apologise for.

The combination that works

The two are not competitors. A sensible setup puts the permanent layer in custom instructions and the conditional layer in skills.

Custom instructions

Identity, tone, units, standing constraints. Short enough to fit reliably.

Skills

Each specific workflow as its own skill with its own folder and trigger description.

Validator

Check each SKILL.md before uploading. The folder-name match is the one that fails silently.

That gives you a small always-on layer that never has to be edited to accommodate a new project, and a set of skills you can add, test, and remove independently.

If you built a skill for something that should have been an instruction

Not a problem, but worth fixing while the site is still relevant to you. Signs the skill is doing the wrong job:

Symptom	Likely cause
The skill fires on almost every message	Its description is too broad. Widen the trigger conditions or move it to custom instructions.
You never see it fire	Its description is too narrow, or the folder name does not match.
You keep editing it for unrelated projects	It holds more than one job. Split it into separate skills.
You enabled it once and forgot about it	It probably belongs in custom instructions.

The not triggering page has the full diagnosis for the second row.

Common questions

Can I use custom instructions and skills together?

Yes, and that is the recommended setup. Custom instructions apply first, skills add situational detail when relevant. Keep the always-on layer short.

Do skills work in the Gemini mobile app?

Skills depend on the surface being used, not the device. The Gemini App and Workspace have separate skill systems, and each needs its own upload. The Gems vs Skills page covers the scope differences in detail.

How many skills can be active at once?

Up to 100 active, with 100 MB of uploads in total. Past the limit, newly uploaded skills may not become active. Both figures are on the format reference page.

Why does my skill never activate?

Two causes dominate. The folder name does not match the name field, which is silent, or the description is too vague to match anything. The validator checks the first; this page fixes the second.

Are custom instructions affected by the Gems shutdown?

No. They are a separate feature and are unaffected. The skills-vs-gems comparison covers what does change.

Should I put everything in a skill instead?

No. Always-on preferences cost you nothing to keep in custom instructions and work better there. Skills are for conditional behaviour.

App vs Workspace →The other surface, and its separate upload. Description examples →The other half of triggering. Gems vs Skills →Storage, activation, and what survives November. Validate a SKILL.md →Catch the folder mismatch before upload. Format reference →Fields, limits, file types.