mixins

Vovk.ts OpenAPI mixins

Mixins turn any OpenAPI 3.x spec into typed client module behaving exactly like native Vovk RPC module — same { params, query, body } call shape, same client surface, same type-inference helpers (VovkBody, VovkOutput, …). Can run mixins standalone (no Next.js) as pure codegen tool.

One caveat not obvious from call shape: mixins work with deriveTools for OpenAI / Anthropic / Vercel function-calling — parameters (JSON Schema) populates from the mixin's validation. Exception: the mcp-handler path reads inputSchemas (Standard Schemas), which mixins don't carry — for MCP servers, wrap mixin calls in createTool instead. Verified in packages/vovk/src/client/createRPC.ts:178-193 (no definition) vs packages/vovk/src/tools/deriveTools.ts:113-115 (reads definition for inputSchemas) and packages/vovk/src/validation/withValidationLibrary.ts:281 (definition set only by procedure({...}).handle(...)). See tools skill for createTool wrapper pattern.

Prefer the official SDK when one exists

Recommend official client library first. Hand-maintained SDKs like stripe, @octokit/rest, @aws-sdk/*, @google-cloud/* ship with auth flows, retries, pagination helpers, webhook signature verification, edge-case handling that generated client can't match — and track upstream API changes faster than any spec snapshot. If vendor publishes official SDK, use it.

Mixins right tool when:

• No official SDK exists — internal services, niche vendors, legacy APIs that only publish OpenAPI document.
• LLM tool exposure — deriveTools works directly for OpenAI / Anthropic / Vercel function-calling. For MCP, wrap mixin calls in createTool({...}) (see caveat at top). For GitHub-style APIs @octokit/rest still better tool body, but mixin remains useful when third-party API has no official SDK.
• Spec-as-source-of-truth — internal microservices where OpenAPI doc is generated and you want client drift to surface as TypeScript error at build time.

For everything else (Stripe charges, S3 uploads, Octokit pagination), reach for official package.

Scope

Covers:

• Declaring mixins under outputConfig.segments.<name>.openAPIMixin.
• source variants: remote URL (with fallback), local file, inline object.
• getModuleName / getMethodName — preset strategies + function form.
• apiRoot + authorization via withDefaults.
• Per-mixin fetcher + AJV strict-mode loosening for messy specs.
• Mixins namespace for components/schemas types.
• Composed vs segmented output (pointer to rpc skill).
• LLM tool exposure: deriveTools direct for function-calling; createTool wrapper for MCP (pointer to tools skill).

Out of scope:

• Authoring own procedures → procedure skill.
• RPC client call shape, customFetcher, per-call init → rpc skill.
• AI tool derivation details → tools skill.
• Writing OpenAPI specs by hand — this skill consumes them.

Declaring a mixin

Mixin declared as pseudo-segment under outputConfig.segments.<name>.openAPIMixin. Key (petstore below) becomes segment folder name in segmented-client mode. Generated module name comes from getModuleName (default 'api'), not from segment key.

// @ts-check
/** @type {import('vovk').VovkConfig} */
const config = {
  outputConfig: {
    imports: {
      validateOnClient: 'vovk-ajv', // optional client-side validation
    },
    segments: {
      petstore: {
        openAPIMixin: {
          source: {
            url: 'https://petstore3.swagger.io/api/v3/openapi.json',
            fallback: './.openapi-cache/petstore.json',
          },
          getModuleName: 'PetstoreAPI',
          getMethodName: 'auto',
          apiRoot: 'https://petstore3.swagger.io/api/v3',
        },
      },
    },
  },
};
export default config;

Run npx vovk generate (or keep vovk dev running) → mixin emitted alongside native RPC modules.

import { PetstoreAPI } from 'vovk-client';

const pets = await PetstoreAPI.getPets({ query: { limit: 10 } });

Import path depends on client layout. Code samples here import from 'vovk-client' — default for composed client + js template, re-exported from node_modules/.vovk-client. If project emits composed client into source tree via ts template (composedClient.outDir), import from that path — e.g. @/client. If project uses segmented client, each mixin lives in own folder named after pseudo-segment key — e.g. @/client/petstore. Call shape + types identical across all three. See rpc skill for full comparison.

Source variants

source is object — pick exactly one shape.

{ url, fallback? } — fetched at generate time. Optional fallback path caches last-seen spec locally; if remote URL unreachable on next generate, Vovk reads fallback. Commit fallback to keep CI green when upstream spec host is down.

source: {
  url: 'https://raw.githubusercontent.com/github/rest-api-description/main/descriptions/api.github.com/api.github.com.json',
  fallback: './.openapi-cache/github.json',
}

{ file } — local spec checked into repo. Both JSON + YAML accepted (Vovk sniffs by leading char: { / [ → JSON, else YAML).

source: { file: './openapi/internal.yaml' }

{ object } — inline JS value. Useful when spec built or transformed by another tool in same project.

import spec from './openapi/internal.json' with { type: 'json' };
// ...
openAPIMixin: { source: { object: spec }, ... }

Module and method naming

getModuleName controls JS name of generated module; getMethodName controls each method. Both accept preset string or function.

Preset strings — getModuleName:

Value	Effect
'api' (default)	Every operation goes into single api module.
any other literal (e.g. 'PetstoreAPI')	Hard-coded single module name — useful for small third-party APIs.

Preset strings — getMethodName:

Value	Effect
'camel-case-operation-id'	Always camelCase the operationId. Throws if operationId missing. Use only when every operation has one.
'auto' (default)	One mode handles all cases: pass operationId through if already camelCase, camelCase it if snake_case, otherwise synthesize from METHOD + path. Safe for messy specs.

'auto' is itself the auto-detecting mode — no separate layer picks between two presets. Reach for 'camel-case-operation-id' only when you want throw-on-missing behavior; otherwise leave default. For more structured needs (splitting operations across multiple modules, custom prefixes), use function — see below.

Function form — receives { operationObject, method, path, openAPIObject }, returns string. Use when operation IDs are structured + you want to split into multiple modules. GitHub REST API is canonical example for the technique (issues/list-for-org → GithubIssuesAPI.listForOrg) — though for actual GitHub work, prefer @octokit/rest over a mixin:

import camelCase from 'lodash/camelCase.js';
import startCase from 'lodash/startCase.js';

openAPIMixin: {
  source: { url: '...', fallback: '...' },
  getModuleName: ({ operationObject }) => {
    const [ns] = operationObject.operationId?.split('/') ?? ['unknown'];
    return `Github${startCase(camelCase(ns)).replace(/ /g, '')}API`;
  },
  getMethodName: ({ operationObject }) => {
    const [, name] = operationObject.operationId?.split('/') ?? ['', 'ERROR'];
    return camelCase(name);
  },
},

Result: GithubIssuesAPI.listForOrg, GithubReposAPI.removeStatusCheckContexts, etc. — imported from generated client like any native module.

apiRoot and authorization

apiRoot sets default base URL for mixin. Required if OAS document has no servers property; if document has servers, Vovk picks first entry unless overridden.

For auth, prefer withDefaults over per-call plumbing. Every generated API module exposes withDefaults({ init?, apiRoot? }), returns new module with options deeply merged into every call:

import { PetstoreAPI } from 'vovk-client';

const PetstoreAPIWithAuth = PetstoreAPI.withDefaults({
  init: { headers: { Authorization: `Bearer ${process.env.PETSTORE_TOKEN}` } },
  apiRoot: 'https://api.example.com', // optional override
});

await PetstoreAPIWithAuth.updatePet({ body: { name: 'Doggo' } });

Also preferred pattern when wrapping mixin in createTool for LLM exposure — wrap module with withDefaults first so LLM-triggered calls go out authenticated, then call from inside tool's execute.

Per-call override fine for one-off cases:

await PetstoreAPI.getPetById({
  params: { petId: 1 },
  apiRoot: 'https://staging.example.com',
  init: { headers: { Authorization: `Bearer ${token}` } },
});

Never embed API secrets in browser bundle. Keep authorized calls server-side (server components, route handlers, server actions, controllers, services), or proxy through your own Vovk segment + add auth header there.

Per-mixin fetcher and AJV tuning

For auth needing dynamic logic (token refresh, signing), use custom fetcher scoped to mixin's segment. Fetcher runs request, performs client-side validation, prepares headers — see rpc skill for full contract.

outputConfig: {
  segments: {
    petstore: {
      openAPIMixin: { /* ... */ },
      imports: { fetcher: './src/lib/petstoreFetcher' },
    },
  },
},

Third-party specs often include non-standard keywords that trip AJV's strict mode. Loosen globally:

libs: {
  /** @type {import('vovk-ajv').VovkAjvConfig} */
  ajv: { options: { strict: false } },
},

Client-side validation opt-out per call:

await PetstoreAPI.getPetById({
  params: { petId: 1 },
  disableClientValidation: true,
});

Type inference and the Mixins namespace

Mixin modules support same inference helpers as native RPC:

import type { VovkBody, VovkQuery, VovkParams, VovkOutput } from 'vovk';
import { PetstoreAPI } from 'vovk-client';

type Body = VovkBody<typeof PetstoreAPI.updatePet>;
type Output = VovkOutput<typeof PetstoreAPI.getPetById>;

Named types from components/schemas across all mixins exposed under Mixins namespace export. Prefer this when third-party spec properly names its components:

import { PetstoreAPI, type Mixins } from 'vovk-client';

const pet: Mixins.Pet = { id: 1, name: 'Doggo' };

For specs that don't populate components/schemas, fall back to VovkOutput<typeof Module.method> — Vovk infers shape from inline response schema instead of synthesized names like ApiUsersIdPost200Response.

With deriveTools

Mixin modules feed deriveTools identically to native RPC modules for function-calling paths. Operation summary, description, operationId populate derived tool's metadata → LLM gets usable description straight from third-party spec.

import { deriveTools } from 'vovk';
import { GithubIssuesAPI, PetstoreAPI } from 'vovk-client';

const { tools } = deriveTools({
  modules: {
    // Wrap with withDefaults to bake in the auth header
    AuthorizedGithubIssuesAPI: GithubIssuesAPI.withDefaults({
      init: {
        headers: {
          Authorization: `Bearer ${process.env.GITHUB_TOKEN}`,
          'X-GitHub-Api-Version': '2022-11-28',
        },
      },
    }),
    PetstoreAPI,
  },
});

MCP exception: mcp-handler reads inputSchemas (Standard Schemas), which mixins lack. For MCP servers exposing mixin endpoints, wrap calls in createTool instead — see tools skill. Function-calling paths (OpenAI / Anthropic / Vercel) work fine — they read parameters (JSON Schema), populated from mixin's validation.

See tools skill for full provider-wiring pipeline (OpenAI / Anthropic / MCP).

Composed vs segmented output

Mixins emit into same client layouts as native RPC. Three TypeScript import paths:

Layout	Import path	Notes
Composed + js template (default)	import { PetstoreAPI } from 'vovk-client'	Emitted to node_modules/.vovk-client, re-exported by vovk-client package. Best for most apps.
Composed + ts template	import { PetstoreAPI } from '@/client'	Uncompiled TypeScript emitted to composedClient.outDir (e.g. ./src/client or ./src/lib/client). Import from that path.
Segmented	import { PetstoreAPI } from '@/client/petstore'	Folder-per-segment under segmentedClient.outDir (default ./src/client). Pseudo-segment key from outputConfig.segments.<name> becomes folder name — petstore, github, etc.

All three share identical call shape + identical types — pick by emission preference. Full comparison in rpc skill.

Python and Rust templates (see python / rust skills) also support mixins.

Flows

"Let the LLM call the Petstore API"

1. Add Petstore OpenAPI as pseudo-segment mixin in vovk.config.mjs.
2. npx vovk generate (or keep vovk dev running).
3. deriveTools({ modules: { PetstoreAPI } }) — wrap with withDefaults if you need auth.
4. Feed to chat loop. See tools skill.

"Wrap an internal REST service we don't own"

1. Export service's OpenAPI spec, host it, or pin snapshot to ./openapi/.
2. Declare mixin with source: { url, fallback } (or { file } for snapshot).
3. Set apiRoot — required unless spec has servers.
4. Add imports.fetcher on segment if auth needs dynamic logic; otherwise wrap with withDefaults at call site.

"My mixin spec has non-standard keywords that break AJV"

Set libs.ajv.options.strict = false. If specific operations still misbehave, pass disableClientValidation: true at call site.

"Module names look awful from auto-generated operation IDs"

Switch to function getModuleName / getMethodName parsing operation ID the way spec structures it. See GitHub example above — split on delimiter, camelCase each part.

"Bundle the mixin as a publishable SDK"

After configuring mixins, vovk bundle treats them like any other generated module. See bundle skill.

Gotchas

• apiRoot required when spec has no servers. Vovk errors at generate time if neither present. Adding apiRoot at call site works, but bake into config for single source of truth.
• fallback is write-through cache. Every successful remote fetch overwrites fallback file — commit it so CI has working snapshot when upstream host flaky.
• Module name is getModuleName, not segment key. Segment key determines segmented-client folder only. outputConfig.segments.petstore.openAPIMixin.getModuleName = 'PetstoreAPI' → import PetstoreAPI, not petstore.
• CORS from browser. Third-party APIs rarely allow direct calls from browser origin. Route through server component, route handler, server action — or add proxy segment + point mixin at it.
• Auth secrets stay server-side. Use withDefaults in server file (Route Handler, Server Action, server component), not in client code shipping to browsers.
• AJV strict mode trips on real-world specs. If generation errors with strict mode: messages, loosen via libs.ajv.options.strict = false.
• Operation IDs drive everything. Spec with missing or duplicate operationIds produces synthesized method names. Complain to upstream owner, or write function getMethodName falling back to METHOD + path.
• Standalone codegen works without Next.js. Install vovk-cli globally (npm i -g vovk-cli) plus vovk + vovk-ajv as deps, run npx vovk generate. No Next.js, no segments directory required — just config file with mixins.