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.
npx agentmods add skills/microsoft/vscode-copilot-chat/agent-customizationnpx skills add microsoft/vscode-copilot-chat --skill agent-customizationgit clone --depth 1 https://github.com/microsoft/vscode-copilot-chatWhat 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 | $0.00193 | $0.01201 |
| Opus 5 | $0.00097 | $0.00600 |
| Sonnet 5 | $0.00039 | $0.00240 |
| Haiku 4.5 | $0.00019 | $0.00120 |
Grade A, and why
agent-customization 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 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.
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.
How it starts
The opening of the file, as written. The whole thing — 83 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Customization
Decision Flow
| Primitive | When to Use |
|---|---|
| Workspace Instructions | Always-on, applies everywhere in the project |
| File Instructions | Explicit via applyTo patterns, or on-demand via description |
| MCP | Integrates external systems, APIs, or data |
| Hooks | Deterministic shell commands at agent lifecycle points (block tools, auto-format, inject context) |
| Custom Agents | Subagents for context isolation, or multi-stage workflows with tool restrictions |
| Prompts | Single focused task with parameterized inputs |
| Skills | On-demand workflow with bundled assets (scripts/templates) |
Quick Reference
Consult the reference docs for templates, domain examples, advanced frontmatter options, asset organization, anti-patterns, and creation checklists. If the references are not enough, load the official documentation links for each primitive.
| Type | File | Location | Reference |
|---|---|---|---|
| Workspace Instructions | copilot-instructions.md, AGENTS.md |
.github/ or root |
Link |
| File Instructions | *.instructions.md |
.github/instructions/ |
Link |
| Prompts | *.prompt.md |
.github/prompts/ |
Link |
| Hooks | *.json |
.github/hooks/ |
Link |
| Custom Agents | *.agent.md |
.github/agents/ |
Link |
| Skills | SKILL.md |
.github/skills/<name>/, .agents/skills/<name>/, .claude/skills/<name>/ |
Link |
User-level: {{VSCODE_USER_PROMPTS_FOLDER}}/ (*.prompt.md, *.instructions.md, *.agent.md; not skills)
Customizations roam with user's settings sync
Creation Process
If you need to explore or validate patterns in the codebase, use a read-only subagent. If the ask-questions tool is available, use it to interview the user and clarify requirements.
Follow these steps when creating any customization file.
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 83 lines · 193 tokens per session scan A 01a307c8386c
agent-customization is a skill published in the GitHub repository microsoft/vscode-copilot-chat (9,977 stars, last pushed 3mo ago), licensed MIT. It adds 193 tokens to every session and 1,201 once invoked, about $0.0010 per session on Opus 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 2026-08-30.
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