create-gemini-agent

A guide for creating a custom Gemini agent in a Markdown file. Gemini is Google’s family of AI models, and an agent is configured with instructions, tools, and settings.

In plain words
What is it for?
Use it to define a Gemini agent’s system prompt, tools, and configuration.
Why use it?
It provides a defined place to describe how the custom agent should behave and what it can use.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/andrader/jup/create-gemini-agent
Any agent
npx skills add andrader/jup --skill create-gemini-agent
Clone the repo
git clone --depth 1 https://github.com/andrader/jup

Made for: Claude Code, Codex.

Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,726 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin unknown No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00026 $0.02726
Opus 5 $0.00013 $0.01363
Sonnet 5 $0.00005 $0.00545
Haiku 4.5 $0.00003 $0.00273

Measured 2d ago against content hash 11ab2bcb0657, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

create-gemini-agent scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Unrestricted tool accessmediumExcessive agency

A wildcard tool grant or "run any command" leaves no least-privilege boundary at all.

- `mcp_*`: Grant access to all tools from all connected MCP servers.
skills/create-gemini-agent/SKILL.md · 342 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 342 lines · 26 tokens per session scan B 11ab2bcb0657

Subscribe to this mod's changes

create-gemini-agent is a skill published in the GitHub repository andrader/jup (15 stars, last pushed 24d ago), with no licence file. It adds 26 tokens to every session and 2,726 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it B with 1 finding (unrestricted tool access). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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