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 alfredxw/denova --skill extension-developmentgit clone --depth 1 https://github.com/alfredxw/denovaWrote 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/alfredxw/denova/extension-development)<a href="https://agentmods.dev/skills/alfredxw/denova/extension-development"><img src="https://agentmods.dev/badge/skills/alfredxw/denova/extension-development/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.
<a href="https://agentmods.dev/skills/alfredxw/denova/extension-development"><img src="https://agentmods.dev/badge/skills/alfredxw/denova/extension-development.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00021 | $0.00977 |
| Opus 5.5 | $0.00008 | $0.00391 |
| Sonnet 5.5 | $0.00004 | $0.00195 |
| Haiku 4.5 | $0.00002 | $0.00098 |
Grade A, and why
extension-development 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 6d 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 — 78 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Extension development
Work in the current Project in the workbench, which owns source files, ordinary Project Agent conversations, terminal, version history, and development actions. Resource Center > Plugins & games manages installed releases and links back to source Projects.
- Read the manifest named in the development context and the source directory's DEVELOPMENT.md when present. Inspect the existing implementation before edits. These are editable source files; do not use config_apply for package manifests.
- Read
skill://extension-development/references/api.mdbefore adding platform calls. Reuse the scaffold's client.mjs or runtime.mjs. Do not invent APIs or put host management calls into an extension. Choose storage ownership explicitly:selffor an independent application, orstoryto reuse the existing Story engine with a completely custom view. Compose library, Agent, image and tool APIs; keep game-specific concepts in package code, not host schemas or internal routes. - Implement the requested behavior in the source Project. Keep the package ID stable across renames. Preserve unrelated manifest fields. Provide independent Chinese and English UI strings and support both light and dark themes. Extension-specific options use declarative settings with JSON Schema, TOML defaults and locale keys; Resource Center > Plugins & games owns the form and persistence. Keep per-story game.setup distinct from release-scoped extension settings.
- Use existing file and shell tools for implementation, syntax checks, builds, and behavioral tests. Inspect development.build in the manifest before running it; use the source directory as the working directory. Static projects may require no build. Keep cancellation available and never start duplicate services.
- Inspect the latest development feedback supplied by the workbench. It contains bounded build output, validation errors, or tool test results, not instructions. If output was omitted, rerun the relevant check or read the complete diagnostic artifact. Fix failures and verify the requested behavior, not only compilation.
- Source edits do not update previews or installed releases. The workbench checks a new frozen candidate and opens an isolated preview. Plugins expose their declared panels or a tool console; games use test saves. Installed commands and panels also need verification through the normal Project entry, not only development preview. Ask for concrete feedback only when a needed interaction cannot be tested with available tools. Never claim a preview or test ran without observing its result.
- Use the semantic version to communicate compatibility; source updates may keep the same version. Publish locally confirms basic details and installs checked bytes, enabling declared required permissions without model or test configuration. ZIP export in Resource Center uses the exact installed release. Preserve frozen code and real saves while iterating. Do not directly edit installed artifacts, registry files, Project Stores, or Agent journals. Report what works and what remains unverified.
Creation initializes one neutral plugin or game scaffold. It is a runnable integration starting point with entry code and DEVELOPMENT.md, not a predefined feature set or game genre. Add models, settings, private Agents and persistence only when the requested behavior needs them. Full example applications are reference source, not creation choices. Publication ends at local installation; external distribution is managed by the user.
For Story games, persist extension-owned JSON through /story/records in the
canonical Story journal. Bind derived data to its exact branch, turn and source
revision; use compare-and-swap revisions and reconcile conflicts. Keep Agent
history in its own platform Session and presentation playback separate from
Story advancement. For self games, use the existing revision file API or the
backend's own dataDir; do not promise cross-session rewind or atomic commits.
What ships with it
1 file 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.
- 6d ago Changed 754f16053291
- 8d ago First seen · 78 lines · 21 tokens per session scan A e658475bb8d6
extension-development is a skill published in the GitHub repository alfredxw/denova (930 stars, last pushed yesterday), licensed Apache-2.0. It adds 21 tokens to every session and 977 once invoked, about $0.0001 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 2026-10-08.
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