Use it when scaffolding GitHub Copilot agents, orchestrators, or subagents in a repository.

It helps you choose the right agent type and organize its instructions, state, handoffs, and quality checks.

How markharrison/IAG-CustomAgent-Labs-OLD configures GitHub Copilot

Q: What is IAG-CustomAgent-Labs-OLD custom-agent.instructions.md?

A guide for creating custom agent definition files for GitHub Copilot, Microsoft's coding assistant.

Reuse

Borrowing it

Nothing to install: this file belongs to markharrison/IAG-CustomAgent-Labs-OLD. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/markharrison/IAG-CustomAgent-Labs-OLD/main/.github/instructions/custom-agent.instructions.md

Clone the repo

git clone --depth 1 https://github.com/markharrison/IAG-CustomAgent-Labs-OLD

Made for: GitHub Copilot.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/markharrison/iag-customagent-labs-old/custom-agent/github.svg)](https://agentmods.dev/instructions/markharrison/iag-customagent-labs-old/custom-agent)

Your own site

<a href="https://agentmods.dev/instructions/markharrison/iag-customagent-labs-old/custom-agent"><img src="https://agentmods.dev/badge/instructions/markharrison/iag-customagent-labs-old/custom-agent/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/markharrison/iag-customagent-labs-old/custom-agent"><img src="https://agentmods.dev/badge/instructions/markharrison/iag-customagent-labs-old/custom-agent.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 13,647 This file is loaded in full into every session.

When invoked 13,647 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original 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.

Model	Per session	Once invoked
Fable 5.1	$0.13647	$0.13647
Opus 5.5	$0.05459	$0.05459
Sonnet 5.5	$0.02729	$0.02729
Haiku 4.5	$0.01365	$0.01365

Measured 2mo ago against content hash ec4131898f03, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

IAG-CustomAgent-Labs-OLD custom-agent.instructions.md scanned grade A with 0 findings 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 2mo 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/instructions/custom-agent.instructions.md · 1,594 lines

How it starts

The opening of the file, as written. The whole thing — 1,594 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Custom Agent Definition Guide

How to create well-structured, maintainable custom agent files for GitHub Copilot. This guide covers three agent archetypes — Agent, Orchestrator, and Subagent — with conventions for frontmatter, body structure, state management, and quality gates.

Official docs: https://docs.github.com/en/copilot/how-tos/use-copilot-agents

Agent Archetypes

Every agent falls into one of three archetypes. Choose the right one before writing anything.

	Agent	Orchestrator	Subagent
Purpose	Self-contained task	Coordinates a pipeline	Executes one pipeline step
User-invocable	✅ Yes	✅ Yes	❌ No
Delegates work	No	Yes (to subagents)	No
Writes state files	✅ Yes (progress)	Yes (pipeline state)	Yes (step output MD)
Writes deliverables	Optional	No	Optional
Owns approval gates	No	Yes	No
Maintains state	Yes (checkpoints)	Yes (via state folder)	No
Has handoffs	Optional	No	No
Location	`.github/agents/`	`.github/agents/`	`.github/agents/_subagents/`

When to use each

Agent: A single agent that does one job end-to-end. No pipeline, no coordination. REQUIRED: Write a state file to ./output/state/00-{agent-name}.md at startup (before Phase 1) with all phases unchecked. Update it after each phase.
Orchestrator: A multi-step workflow where each step needs a specialist agent, human approval between steps, and the ability to resume, revert, or stop. REQUIRED: Write 00-{orchestrator-name}.md to track pipeline state, parameters, and step checkboxes.
Subagent: A specialist that handles one step in an orchestrator's pipeline. Never invoked directly by users. REQUIRED: Write a step state file ({NN}-{step}.md) at startup with all phases unchecked. Update it progressively after each phase.

Read the full file on GitHub · 1,594 lines

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.

2mo ago First seen · 1,594 lines · 13,647 tokens per session scan A ec4131898f03

Subscribe to this mod's changes

IAG-CustomAgent-Labs-OLD custom-agent.instructions.md is an instructions file published in the GitHub repository markharrison/IAG-CustomAgent-Labs-OLD (2 stars, last pushed 7mo ago), licensed MIT. It adds 13,647 tokens to every session, about $0.0546 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Building agents

IAG-CustomAgent-Labs-OLD custom-agent.instructions.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
IAG-CustomAgent-Labs-OLD custom-agent.instructions.mdmarkharrison/IAG-CustomAgent-Labs-OLD	Instructions file	2	7mo ago	MIT	A	13,647	GitHub Copilot
vscode buildNext.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	9,719	GitHub Copilot
next.js AGENTS.mdvercel/next.js	Instructions file	143k	yesterday	MIT	A	7,461	Codex, OpenCode
langchain AGENTS.mdlangchain-ai/langchain	Instructions file	149k	yesterday	MIT	A	4,680	Codex, OpenCode
vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

IAG-CustomAgent-Labs-OLD: Instructions file for GitHub Copilot