Host Pattern

What it does

When your agent uses it

• Adding a new domain to Nuclears plugin system
• Implementing a host
• Phrases include add a domain
• Host implementation

Example prompts

• “add a domain”
• “new domain”
• “host implementation”
• “/host-pattern”

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

1. 1Host type - the contract (SDK, no implementation)
2. 2API class - what plugins actually call (SDK, wraps the host)
3. 3Host implementation - bridges the API to player internals (player)

What it can do on your machine

Read from SKILL.md and the folder at commit 27904e9. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are typescript).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Host Pattern loads about 1.3k tokens when it runs. Until then it costs about 107 tokens; SKILL.md has 264 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~107

When it runs · the whole SKILL.md, loaded when a task matches

~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from nukeop/nuclear at commit 27904e9, republished under its AGPL-3.0 licence (© nukeop). 264 words, ~1,327 tokens.

name

host-pattern

description

Use when adding a new domain to Nuclear's plugin system, or implementing a host. Covers the host pattern (how player functionality is exposed to plugins), the host interface and API class structure, how hosts are implemented in the player, error handling conventions, and what files to create and modify. Trigger phrases include "add a domain", "new domain", "host implementation", "host pattern", "createPluginAPI".

// packages/plugin-sdk/src/api/yourDomain.ts
export class YourDomainAPI {
  #host?: YourDomainHost;

  constructor(host?: YourDomainHost) {
    this.#host = host;
  }

  #withHost<T>(fn: (host: YourDomainHost) => T): T {
    const host = this.#host;
    if (!host) {
      throw new Error('YourDomain host not available');
    }
    return fn(host);
  }

  yourMethod(arg: SomeType) {
    return this.#withHost((host) => host.yourMethod(arg));
  }
}

// packages/plugin-sdk/src/api/index.ts
import type { YourDomainHost } from '../types/yourDomain';
import { YourDomainAPI } from './yourDomain';

// Add to class:
readonly YourDomain: YourDomainAPI;

// Add to constructor opts type:
yourDomainHost?: YourDomainHost;

// Add to constructor body:
this.YourDomain = new YourDomainAPI(opts?.yourDomainHost);

// packages/player/src/services/plugins/createPluginAPI.ts
import { yourDomainHost } from '../../services/yourDomainHost';
// Add to NuclearPluginAPI constructor call:
yourDomainHost,

// packages/player/src/services/yourDomainHost.ts
import type { YourDomainHost } from '@nuclearplayer/plugin-sdk';
import { useYourDomainStore } from '../stores/yourDomainStore';

export const createYourDomainHost = (): YourDomainHost => ({
  yourMethod: (arg) => useYourDomainStore.getState().doThing(arg),
  getState: () => useYourDomainStore.getState().value,
});

export const yourDomainHost = createYourDomainHost();

const getProvider = (providerId?: string) =>
  providersHost.get<YourProvider>(
    providerId ?? providersHost.getActive('yourkind'), 'yourkind',
  );

export const createYourDomainHost = (): YourDomainHost => ({
  async fetch(query, providerId?) {
    const provider = getProvider(providerId);
    if (!provider) throw new Error('No provider available');
    return provider.fetch(query);
  },
});

export const createYourDomainHost = (): YourDomainHost => ({
  async fetchAll() {
    const providers = providersHost.list('yourkind') as YourProvider[];
    const results = await Promise.allSettled(providers.map(async (provider) => {
      const items = await provider.fetch();
      return { providerId: provider.id, providerName: provider.name, items };
    }));
    return results.filter(isFulfilled).map((r) => r.value);
  },
});

© nukeop, AGPL-3.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/host-pattern of nukeop/nuclear.

Open the folder on GitHubat commit 27904e9