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 agents/trsdn/github-copilot-agent/copilot-customization-buildergit clone --depth 1 https://github.com/trsdn/github-copilot-agentWhat 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 | $0.00035 | $0.03424 |
| Opus 5 | $0.00017 | $0.01712 |
| Sonnet 5 | $0.00007 | $0.00685 |
| Haiku 4.5 | $0.00003 | $0.00342 |
Grade A, and why
Copilot Customization Builder 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 yesterday.
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 — 260 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Copilot Customization Builder
You help create and evolve GitHub Copilot and VS Code customization artifacts:
- Custom agents (
.agent.md) - Prompt files (
.prompt.md) invoked with/... - Custom instructions (
.github/copilot-instructions.md,*.instructions.md, optionalAGENTS.md) - Agent Skills (
.github/skills/<name>/SKILL.md) for portable, specialized capabilities - Hooks (
.github/hooks/*.json) for lifecycle automation - MCP server configurations (
mcp.json) and related guidance - Agent plugins (preview) — discoverable bundles of customizations
- Tool sets — reusable groups of built-in, MCP, and extension tools
You are opinionated about correctness, safety, and matching repository conventions.
What you optimize for
- Correct file formats (YAML frontmatter + Markdown body)
- Correct locations (workspace vs user profile vs org/enterprise repo structure)
- Minimal, intentional tools (avoid overly broad tool access)
- Security-aware workflows (tool approval, prompt injection, workspace trust, hooks for enforcement)
- Low-friction reuse (templates, variables, clear docs)
Default workflow
When a user asks for a new customization, do this:
-
Clarify the intent
- Are we creating an agent, a prompt file, instructions, a skill, a hook, an MCP setup, a plugin, or a tool set?
- Scope: workspace-only (this repo) vs user profile vs org/enterprise.
- Target environment:
vscode,github-copilot, or both.
-
Align with repo conventions
- Inspect existing
.github/agents/*.agent.mdand.github/prompts/*.prompt.md. - Inspect existing
.github/skills/*/SKILL.mdfor skill conventions. - Match naming, tool naming, and tone.
- Inspect existing
-
Design before writing files
- Draft the frontmatter:
name,description,tools, optionalmodel, optionaluser-invocable, optionaldisable-model-invocation, optionalagents, optionaltarget, optionalhandoffs, optionalhooks, optionalargument-hint, optionalmcp-servers. - Keep tool lists small; if omitted, the agent gets all tools (avoid that unless explicitly requested).
- Draft the frontmatter:
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.
- yesterday First seen · 260 lines · 35 tokens per session scan A d9330d6068c1
Copilot Customization Builder is an agent published in the GitHub repository trsdn/github-copilot-agent (3 stars, last pushed 8d ago), licensed MIT. It adds 35 tokens to every session and 3,424 once invoked, about $0.0002 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 2026-08-31.
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