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# Writing Genkit plugins Firebase Genkit's capabilities are designed to be extended by plugins. Genkit plugins are configurable modules that can provide models, retrievers, indexers, trace stores, and more. You've already seen plugins in action just by using Genkit: ```golang import { {% includecode github_path="firebase/genkit/go/internal/doc-snippets/models.go" region_tag="import" %} } ``` ```golang {% includecode github_path="firebase/genkit/go/internal/doc-snippets/models.go" region_tag="init" adjust_indentation="auto" %} ``` The Vertex AI plugin takes configuration (such as the user's Google Cloud project ID) and registers a variety of new models, embedders, and more with the Genkit registry. The registry serves as a lookup service for named actions at runtime, and powers Genkit's local UI for running and inspecting models, prompts, and more. ## Creating a plugin In Go, a Genkit plugin is simply a package that adheres to a small set of conventions. A single module can contain several plugins. ### Provider ID Every plugin must have a unique identifier string that distinguishes it from other plugins. Genkit uses this identifier as a namespace for every resource your plugin defines, to prevent naming conflicts with other plugins. For example, if your plugin has an ID `yourplugin` and provides a model called `text-generator`, the full model identifier will be `yourplugin/text-generator`. You don't need to export your provider ID, but you should define it once for your plugin and use it consistently when required by a Genkit function. ```golang const providerID = "yourplugin" ``` ### Standard exports Every plugin should define and export the following symbols: - An `Init()` function with a declaration like the following: ```golang func Init(ctx context.Context, cfg *Config) (err error) ``` Omit any parameters you don't use (for example, you might not have a `cfg` parameter if your plugin does not provide any plugin-wide configuration options). In this function, perform any setup steps required by your plugin. For example: - Confirm that any required configuration values are specified and assign default values to any unspecified optional settings. - Verify that the given configuration options are valid together. - Create any shared resources required by the rest of your plugin. For example, create clients for any services your plugin accesses. To the extent possible, the resources provided by your plugin shouldn't assume that the user has taken any action other than calling `Init`. You should define and export this function even if your plugin doesn't require any initialization. In this case, `Init` can just return a `nil` error. - A `Config` struct type. This type should encapsulate all of the configuration options accepted by `Init`. For any plugin options that are secret values, such as API keys, you should offer both a `Config` option and a default environment variable to configure it. This lets your plugin take advantage of the secret management features offered by many hosting providers (such as Cloud Secret Manager, which you can use with Cloud Run). For example: ```golang {% includecode github_path="firebase/genkit/go/internal/doc-snippets/plugin/plugin.go" region_tag="init" adjust_indentation="auto" %} ``` ## Building plugin features A single plugin can activate many new things within Genkit. For example, the Vertex AI plugin activates several new models as well as an embedder. ### Model plugins Genkit model plugins add one or more generative AI models to the Genkit registry. A model represents any generative model that is capable of receiving a prompt as input and generating text, media, or data as output. See [Writing a Genkit model plugin](plugin-authoring-models). ### Telemetry plugins Genkit telemetry plugins configure Genkit's OpenTelemetry instrumentation to export traces, metrics, and logs to a particular monitoring or visualization tool. See [Writing a Genkit telemetry plugin](plugin-authoring-telemetry). ## Publishing a plugin Genkit plugins can be published as normal Go packages. To increase discoverability, your package should have `genkit` somewhere in its name so it can be found with a simple search on [`pkg.go.dev`](https://pkg.go.dev/search?q=genkit). Any of the following are good choices: - `github.com/yourorg/genkit-plugins/servicename` - `github.com/yourorg/your-repo/genkit/servicename`