Building Provider Plugins

This guide walks through building a provider plugin that adds a model provider (LLM) to FluffBuzz. By the end you will have a provider with a model catalog, API key auth, and dynamic model resolution.

If you have not built any FluffBuzz plugin before, read Getting Started first for the basic package structure and manifest setup.

Walkthrough

Package and manifest

{
  "name": "@myorg/fluffbuzz-acme-ai",
  "version": "1.0.0",
  "type": "module",
  "fluffbuzz": {
    "extensions": ["./index.ts"],
    "providers": ["acme-ai"]
  }
}

The manifest declares providerAuthEnvVars so FluffBuzz can detect credentials without loading your plugin runtime.

A minimal provider needs an id, label, auth, and catalog:

index.ts

import { definePluginEntry } from "fluffbuzz/plugin-sdk/plugin-entry";
import { createProviderApiKeyAuthMethod } from "fluffbuzz/plugin-sdk/provider-auth";

export default definePluginEntry({
  id: "acme-ai",
  name: "Acme AI",
  description: "Acme AI model provider",
  register(api) {
    api.registerProvider({
      id: "acme-ai",
      label: "Acme AI",
      docsPath: "/providers/acme-ai",
      envVars: ["ACME_AI_API_KEY"],

      auth: [
        createProviderApiKeyAuthMethod({
          providerId: "acme-ai",
          methodId: "api-key",
          label: "Acme AI API key",
          hint: "API key from your Acme AI dashboard",
          optionKey: "acmeAiApiKey",
          flagName: "--acme-ai-api-key",
          envVar: "ACME_AI_API_KEY",
          promptMessage: "Enter your Acme AI API key",
          defaultModel: "acme-ai/acme-large",
        }),
      ],

      catalog: {
        order: "simple",
        run: async (ctx) => {
          const apiKey =
            ctx.resolveProviderApiKey("acme-ai").apiKey;
          if (!apiKey) return null;
          return {
            provider: {
              baseUrl: "https://api.acme-ai.com/v1",
              apiKey,
              api: "openai-completions",
              models: [
                {
                  id: "acme-large",
                  name: "Acme Large",
                  reasoning: true,
                  input: ["text", "image"],
                  cost: { input: 3, output: 15, cacheRead: 0.3, cacheWrite: 3.75 },
                  contextWindow: 200000,
                  maxTokens: 32768,
                },
                {
                  id: "acme-small",
                  name: "Acme Small",
                  reasoning: false,
                  input: ["text"],
                  cost: { input: 1, output: 5, cacheRead: 0.1, cacheWrite: 1.25 },
                  contextWindow: 128000,
                  maxTokens: 8192,
                },
              ],
            },
          };
        },
      },
    });
  },
});

That is a working provider. Users can now fluffbuzz onboard --acme-ai-api-key <key> and select acme-ai/acme-large as their model.For bundled providers that only register one text provider with API-key auth plus a single catalog-backed runtime, prefer the narrower defineSingleProviderPluginEntry(...) helper:

import { defineSingleProviderPluginEntry } from "fluffbuzz/plugin-sdk/provider-entry";

export default defineSingleProviderPluginEntry({
  id: "acme-ai",
  name: "Acme AI",
  description: "Acme AI model provider",
  provider: {
    label: "Acme AI",
    docsPath: "/providers/acme-ai",
    auth: [
      {
        methodId: "api-key",
        label: "Acme AI API key",
        hint: "API key from your Acme AI dashboard",
        optionKey: "acmeAiApiKey",
        flagName: "--acme-ai-api-key",
        envVar: "ACME_AI_API_KEY",
        promptMessage: "Enter your Acme AI API key",
        defaultModel: "acme-ai/acme-large",
      },
    ],
    catalog: {
      buildProvider: () => ({
        api: "openai-completions",
        baseUrl: "https://api.acme-ai.com/v1",
        models: [{ id: "acme-large", name: "Acme Large" }],
      }),
    },
  },
});

If your auth flow also needs to patch models.providers.*, aliases, and the agent default model during onboarding, use the preset helpers from fluffbuzz/plugin-sdk/provider-onboard. The narrowest helpers are createDefaultModelPresetAppliers(...), createDefaultModelsPresetAppliers(...), and createModelCatalogPresetAppliers(...).

Add dynamic model resolution

If your provider accepts arbitrary model IDs (like a proxy or router), add resolveDynamicModel:

api.registerProvider({
  // ... id, label, auth, catalog from above

  resolveDynamicModel: (ctx) => ({
    id: ctx.modelId,
    name: ctx.modelId,
    provider: "acme-ai",
    api: "openai-completions",
    baseUrl: "https://api.acme-ai.com/v1",
    reasoning: false,
    input: ["text"],
    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
    contextWindow: 128000,
    maxTokens: 8192,
  }),
});

If resolving requires a network call, use prepareDynamicModel for async warm-up — resolveDynamicModel runs again after it completes.

Add runtime hooks (as needed)

Most providers only need catalog + resolveDynamicModel. Add hooks incrementally as your provider requires them.

Token exchange
Custom headers
Usage and billing

For providers that need a token exchange before each inference call:

prepareRuntimeAuth: async (ctx) => {
  const exchanged = await exchangeToken(ctx.apiKey);
  return {
    apiKey: exchanged.token,
    baseUrl: exchanged.baseUrl,
    expiresAt: exchanged.expiresAt,
  };
},

For providers that need custom request headers or body modifications:

// wrapStreamFn returns a StreamFn derived from ctx.streamFn
wrapStreamFn: (ctx) => {
  if (!ctx.streamFn) return undefined;
  const inner = ctx.streamFn;
  return async (params) => {
    params.headers = {
      ...params.headers,
      "X-Acme-Version": "2",
    };
    return inner(params);
  };
},

For providers that expose usage/billing data:

resolveUsageAuth: async (ctx) => {
  const auth = await ctx.resolveOAuthToken();
  return auth ? { token: auth.token } : null;
},
fetchUsageSnapshot: async (ctx) => {
  return await fetchAcmeUsage(ctx.token, ctx.timeoutMs);
},

All available provider hooks

FluffBuzz calls hooks in this order. Most providers only use 2-3:

#	Hook	When to use
1	`catalog`	Model catalog or base URL defaults
2	`resolveDynamicModel`	Accept arbitrary upstream model IDs
3	`prepareDynamicModel`	Async metadata fetch before resolving
4	`normalizeResolvedModel`	Transport rewrites before the runner
5	`capabilities`	Transcript/tooling metadata (data, not callable)
6	`prepareExtraParams`	Default request params
7	`wrapStreamFn`	Custom headers/body wrappers
8	`formatApiKey`	Custom runtime token shape
9	`refreshOAuth`	Custom OAuth refresh
10	`buildAuthDoctorHint`	Auth repair guidance
11	`isCacheTtlEligible`	Prompt cache TTL gating
12	`buildMissingAuthMessage`	Custom missing-auth hint
13	`suppressBuiltInModel`	Hide stale upstream rows
14	`augmentModelCatalog`	Synthetic forward-compat rows
15	`isBinaryThinking`	Binary thinking on/off
16	`supportsXHighThinking`	`xhigh` reasoning support
17	`resolveDefaultThinkingLevel`	Default `/think` policy
18	`isModernModelRef`	Live/smoke model matching
19	`prepareRuntimeAuth`	Token exchange before inference
20	`resolveUsageAuth`	Custom usage credential parsing
21	`fetchUsageSnapshot`	Custom usage endpoint
22	`onModelSelected`	Post-selection callback (e.g. telemetry)

For detailed descriptions and real-world examples, see Internals: Provider Runtime Hooks.

Add extra capabilities (optional)

A provider plugin can register speech, media understanding, image generation, and web search alongside text inference:

register(api) {
  api.registerProvider({ id: "acme-ai", /* ... */ });

  api.registerSpeechProvider({
    id: "acme-ai",
    label: "Acme Speech",
    isConfigured: ({ config }) => Boolean(config.messages?.tts),
    synthesize: async (req) => ({
      audioBuffer: Buffer.from(/* PCM data */),
      outputFormat: "mp3",
      fileExtension: ".mp3",
      voiceCompatible: false,
    }),
  });

  api.registerMediaUnderstandingProvider({
    id: "acme-ai",
    capabilities: ["image", "audio"],
    describeImage: async (req) => ({ text: "A photo of..." }),
    transcribeAudio: async (req) => ({ text: "Transcript..." }),
  });

  api.registerImageGenerationProvider({
    id: "acme-ai",
    label: "Acme Images",
    generate: async (req) => ({ /* image result */ }),
  });
}

FluffBuzz classifies this as a hybrid-capability plugin. This is the recommended pattern for company plugins (one plugin per vendor). See Internals: Capability Ownership.

Test

src/provider.test.ts

import { describe, it, expect } from "vitest";
// Export your provider config object from index.ts or a dedicated file
import { acmeProvider } from "./provider.js";

describe("acme-ai provider", () => {
  it("resolves dynamic models", () => {
    const model = acmeProvider.resolveDynamicModel!({
      modelId: "acme-beta-v3",
    } as any);
    expect(model.id).toBe("acme-beta-v3");
    expect(model.provider).toBe("acme-ai");
  });

  it("returns catalog when key is available", async () => {
    const result = await acmeProvider.catalog!.run({
      resolveProviderApiKey: () => ({ apiKey: "test-key" }),
    } as any);
    expect(result?.provider?.models).toHaveLength(2);
  });

  it("returns null catalog when no key", async () => {
    const result = await acmeProvider.catalog!.run({
      resolveProviderApiKey: () => ({ apiKey: undefined }),
    } as any);
    expect(result).toBeNull();
  });
});

File structure

extensions/acme-ai/
├── package.json              # fluffbuzz.providers metadata
├── fluffbuzz.plugin.json      # Manifest with providerAuthEnvVars
├── index.ts                  # definePluginEntry + registerProvider
└── src/
    ├── provider.test.ts      # Tests
    └── usage.ts              # Usage endpoint (optional)

Catalog order reference

catalog.order controls when your catalog merges relative to built-in providers:

Order	When	Use case
`simple`	First pass	Plain API-key providers
`profile`	After simple	Providers gated on auth profiles
`paired`	After profile	Synthesize multiple related entries
`late`	Last pass	Override existing providers (wins on collision)

Next steps

Channel Plugins — if your plugin also provides a channel
SDK Runtime — api.runtime helpers (TTS, search, subagent)
SDK Overview — full subpath import reference
Plugin Internals — hook details and bundled examples

Overview

Plugins

Skills

Automation

Tools

Agent coordination

Building Provider Plugins

Building Provider Plugins

Walkthrough

File structure

Catalog order reference

Next steps

Overview

Plugins

Skills

Automation

Tools

Agent coordination

​Building Provider Plugins

​Walkthrough

​File structure

​Catalog order reference

​Next steps

Building Provider Plugins

Walkthrough

File structure

Catalog order reference

Next steps