What causes "API not implemented" in mastra-ai/mastra?

Use a concrete toolset subclass that overrides getApiClient and returns the generated client

API not implemented

Error message

API not implemented

What it means

OpenAPIToolset's base implementation of getApiClient throws 'API not implemented'. The toolset can generate tools from its schema without a live client (baseClient defaults to {}), but if you ask for an actual API client, only concrete subclasses that bind a real HTTP client can answer. The error marks the unimplemented capability, not a runtime failure.

Source

Thrown at packages/core/src/integration/openapi-toolset.ts:27

  authType: string = 'API_KEY';

  constructor() {}

  protected get toolSchemas(): any {
    return {};
  }

  protected get toolDocumentations(): Record<string, { comment: string; doc?: string }> {
    return {};
  }

  protected get baseClient(): any {
    return {};
  }

  async getApiClient(): Promise<any> {
    throw new Error('API not implemented');
  }

  protected _generateIntegrationTools<T>() {
    const { client: _client, ...clientMethods } = this.baseClient;
    const schemas = this.toolSchemas;
    const documentations = this.toolDocumentations;

    const tools = Object.keys(clientMethods).reduce((acc, key) => {
      const comment = documentations[key]?.comment;
      // const doc = documentations[key]?.doc;
      const fallbackComment = `Execute ${key}`;

      const tool = createTool({
        id: key,
        inputSchema: schemas[key] || z.object({}),
        description: comment || fallbackComment,
        // documentation: doc || fallbackComment,
        execute: async input => {

View on GitHub (pinned to 75dd419e61)

Solutions

Use a concrete toolset subclass that overrides getApiClient and returns the generated client
If you only need the generated tools, use _generateIntegrationTools output / listTools instead of getApiClient
Construct the API client from the OpenAPI document yourself using the spec you loaded
Extend OpenAPIToolset and override getApiClient to return your bound client

Example fix

// before
const client = await toolset.getApiClient(); // throws
const tools = toolset._generateIntegrationTools(); // use generated tools instead
// after
class MyToolset extends OpenAPIToolset {
  async getApiClient() {
    return createClient(this.openApiSpec);
  }
}
const client = await new MyToolset(spec).getApiClient();

Defensive patterns

Strategy: fallback

Validate before calling

if (toolset.getApiClient === OpenAPIToolset.prototype.getApiClient) {
  // base toolset has no client; use generated tools instead
}

Type guard

function hasApiToolsetClient(toolset) {
  return typeof toolset.getApiClient === 'function' &&
    toolset.getApiClient !== OpenAPIToolset.prototype.getApiClient;
}

Try / catch

try {
  client = await toolset.getApiClient();
} catch (e) {
  if (e.message === 'API not implemented') {
    client = null; // use toolset.listTools() / generated tools instead
  } else {
    throw e;
  }
}

Prevention

Use concrete toolset subclasses that bind a real client
If you only need tools, use the generated integration tools rather than the client
Override getApiClient when subclassing OpenAPIToolset
Check for a client before writing code paths that depend on direct API calls

When it happens

Trigger: Calling toolset.getApiClient() (directly or via the client() helper that invokes it) on a plain OpenAPIToolset / base toolset instance that does not override getApiClient with a real client implementation.

Common situations: Instantiating a generic OpenAPI toolset from a spec and then trying to obtain its client for custom calls; helper code assuming every toolset exposes getApiClient; subclassing OpenAPIToolset without wiring the generated client.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/22492c53f6fdd3b7. Report an issue: GitHub.