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 skills add vinzscam/backstage-skills --skill creating-backstage-plugingit clone --depth 1 https://github.com/vinzscam/backstage-skillsWrote 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.
[](https://agentmods.dev/skills/vinzscam/backstage-skills/creating-backstage-plugin)<a href="https://agentmods.dev/skills/vinzscam/backstage-skills/creating-backstage-plugin"><img src="https://agentmods.dev/badge/skills/vinzscam/backstage-skills/creating-backstage-plugin.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00134 | $0.02575 |
| Opus 5 | $0.00067 | $0.01288 |
| Sonnet 5 | $0.00027 | $0.00515 |
| Haiku 4.5 | $0.00013 | $0.00258 |
Grade A, and why
creating-backstage-plugin 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 8d 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 — 189 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Creating a Backstage Plugin
When to use this skill
The user wants to bootstrap a new plugin in a Backstage repo. Either:
- They've described the plugin in free text ("I want a frontend plugin that lists my groups")
- Or they've asked generically ("scaffold a new plugin") and you should ask what they want
The flow
Always follow these steps in order. Do not run yarn new until after the user confirms the plan in step 3.
1. Capture intent
If the user already described the plugin, parse it. Otherwise ask one question:
"What kind of plugin do you want, and what should it do?"
2. Parse intent into a plan
Map the user's description to:
- packages: one or more package scaffolds. Most plugins are a single package, but connected plugins (a frontend that calls its own dedicated backend) need three: a
frontend-plugin, abackend-plugin, and aplugin-common-libraryfor shared types. See "Connected plugin sets" below for when to propose this. - template (per package): one of the 9 supported templates (see
references/templates.mdfor the full list and selection rules). - id (per package): kebab-case. For connected sets, the three ids share a common base (e.g.
jira+jira-backend+jira-common). - patterns (per package): which pattern skills to invoke post-scaffold. See
references/intent-detection.mdfor keyword → pattern heuristics.
Connected plugin sets
When the user describes a plugin that has both a UI surface AND its own dedicated backend (e.g. "a Jira plugin that shows project info" → it needs a backend to broker the Jira API call AND a frontend to render the result), propose a 3-package set instead of a single template:
| Package | Template | Purpose |
|---|---|---|
<id> |
frontend-plugin |
The UI |
<id>-backend |
backend-plugin |
Backend routes; talks to the upstream system |
<id>-common |
plugin-common-library |
Shared TypeScript types (request/response interfaces, domain models) imported by both sides |
What ships with it
2 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.
- 8d ago First seen · 189 lines · 134 tokens per session scan A 03e83b242660
creating-backstage-plugin is a skill published in the GitHub repository vinzscam/backstage-skills (4 stars, last pushed 13d ago), licensed Apache-2.0. It adds 134 tokens to every session and 2,575 once invoked, about $0.0007 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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