trembita

Lightweight TypeScript HTTP client for consuming third-party JSON APIs. Built on the platform fetch API with strict Result<T, E> error handling — zero legacy dependencies, no request, no Bluebird.

Named after the Carpathian trembita — a long signal horn. One small client, explicit success/failure at a distance.

Quick links: Install · Minimal example · Learning guide · Examples · Agent skill · Why trembita · Use cases · @trembita/openapi · Error handling · API reference · For AI agents · Migration from v1

Install

npm install trembita
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Optional OpenAPI helpers (path expansion, requestOpenapiPath, Standard Schema re-exports) live in @trembita/openapi:

npm install trembita @trembita/openapi
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See packages/openapi/README.md.

Requirements

• Node >= 20.10 (Active LTS recommended).
• Browser: bundler + global fetch and URL (same ESM entry).

Minimal example

Uses throw on bad init so the same snippet works in Node and browsers (no process.exit).

import { createTrembita, HTTP_OK } from 'trembita';

const api = createTrembita({ endpoint: 'https://api.example.com/v1' });
if (!api.ok) throw new Error('Invalid endpoint');

const json = await api.value.request({
  path: '/resource',
  expectedCodes: [HTTP_OK]
});

if (!json.ok) {
  console.error(json.error.kind);
}
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Learning Path

Choose your starting point based on available time:

⚡ Super Quick (2 minutes)

QUICK_START.md — Install, 3-step example, common patterns, error types, FAQ.

🎓 Complete Learning (30 minutes)

LEARNING_GUIDE.md — Core concepts, building clients, error handling, testing, advanced features, patterns.

🏗️ System Design (15 minutes)

ARCHITECTURE.md — Visual diagrams, request pipeline, error flow, feature matrix, integration patterns.

🤔 Right Tool for You? (10 minutes)

DECISION_GUIDE.md — Compare with Axios/Got/Fetch, scenario-based recommendations, migration guides.

💡 Real-World Examples (varies)

EXAMPLES.md — 7+ use cases: GitHub API, payments, microservices, health checks, webhooks, search, backups.

📝 Starter Code

examples/ directory — Copy-paste ready:

• rest-api-client.ts — Complete CRUD client
• testing-with-mock-fetch.test.ts — Unit test patterns
• resilience-patterns.ts — Retries, circuit breaker, failover

See examples/README.md for navigation.

Why trembita

• Type-safe errors — every failure is a tagged discriminated union (error.kind), not a thrown exception. TypeScript narrows the error for you.
• Zero runtime dependencies — uses fetch and URL from the platform. Works in Node >= 20 and browsers (via bundler).
• Tiny API surface — createTrembita() → { request, client }. No classes, no middleware chains, no plugin system.
• Testable by design — inject fetchImpl to swap fetch in unit tests without mocking globals.
• ESM-only, strict TypeScript — ships .d.ts + source maps, tree-shakeable with sideEffects: false.

Use cases

Consuming a REST API in a backend service

When your Node service calls a third-party REST API (payment provider, CRM, shipping tracker), trembita gives you a typed client with predictable error handling instead of scattered try/catch blocks around raw fetch.

import { createTrembita, HTTP_OK } from 'trembita';

const stripe = createTrembita({
  endpoint: 'https://api.stripe.com/v1'
});
if (!stripe.ok) throw new Error('Bad Stripe config');

const charges = await stripe.value.request({
  path: '/charges',
  query: { limit: '10' },
  headers: { Authorization: `Bearer ${process.env.STRIPE_KEY}` },
  expectedCodes: [HTTP_OK]
});

if (!charges.ok) {
  if (charges.error.kind === 'unexpected_status') {
    console.error('Stripe returned', charges.error.statusCode);
  }
}
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Wrapping a microservice-to-microservice call

Internal services often communicate over HTTP JSON. trembita standardizes how you send requests and handle non-200 responses across service boundaries.

const userService = createTrembita({
  endpoint: 'http://user-service.internal:3000'
});
if (!userService.ok) throw new Error('Bad user-service config');

const user = await userService.value.request({
  path: `/users/${userId}`,
  expectedCodes: [HTTP_OK]
});

if (!user.ok && user.error.kind === 'unexpected_status') {
  if (user.error.statusCode === 404) {
    return null;
  }
}
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Health checks and monitoring

Use the lower-level client function when you need the raw status code and body — useful for health checks, readiness probes, or status dashboards.

const raw = await api.value.client({ path: '/health' });
if (raw.ok && raw.value.statusCode === 200) {
  console.log('Service healthy:', raw.value.body);
}
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Browser fetch with a bundler

trembita works in the browser with any bundler (Vite, webpack, esbuild). The same ESM entry point uses the global fetch and URL APIs.

import { createTrembita, HTTP_OK } from 'trembita';

const api = createTrembita({
  endpoint: 'https://api.example.com/v1'
});
if (!api.ok) {
  showError('Failed to initialize API client');
}
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@trembita/openapi (optional)

Use openapi-typescript paths for templates, then expandOpenapiPath or requestOpenapiPath so path mistakes stay in Result before HTTP. The add-on package re-exports validateStandardSchema, requestWithStandardSchema, createRetryingFetch, and traceContextHeaders for one import line. Full notes, bundle spike, and openapi-fetch positioning: packages/openapi/README.md.

Testing with injected fetch

Pass a mock fetchImpl to test your integration layer without touching the network or patching globals.

import { createTrembita, HTTP_OK } from 'trembita';
import { vi } from 'vitest';

const fetchImpl = vi.fn(() =>
  Promise.resolve(new Response(JSON.stringify({ id: 1 }), { status: 200 }))
);

const created = createTrembita({
  endpoint: 'https://api.test.com',
  fetchImpl
});

const result = await created.value.request({
  path: '/items/1',
  expectedCodes: [HTTP_OK]
});

expect(result.ok).toBe(true);
expect(fetchImpl).toHaveBeenCalledOnce();
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Functional style

The API is functional-first: createTrembita returns a Result, then plain client / request functions — no class instance. Failures use tagged errors (error.kind) so callers narrow with types instead of relying on try/catch for normal HTTP outcomes.

This is not pure FP end-to-end: fetch, the network, and logging are ordinary side effects. Think FP-style errors and surface area, not a fully pure program.

Error handling

Every operation returns a Result<T, E> — either { ok: true, value } or { ok: false, error }. Errors are tagged unions you can narrow with error.kind:

error.kind	When
missing_options	No options passed to createTrembita
options_not_object	Options is not an object
missing_endpoint	endpoint field is missing
endpoint_not_string	endpoint is not a string
endpoint_invalid_url	endpoint URL cannot be parsed or bad scheme
invalid_request_options	Missing or invalid path/url in request
fetch_failed	Network error (DNS, timeout, connection reset)
timeout	Request exceeded configured timeout
circuit_open	Circuit breaker is open; request short-circuited
invalid_json	Response body is not valid JSON
unexpected_status	HTTP status not in expectedCodes

API reference

Full TypeDoc documentation is published at oleg-koval.github.io/trembita (core trembita entry only). @trembita/openapi types are published with that package — see packages/openapi/README.md.

createTrembita(options)

Creates a client bound to a base URL.

Option	Type	Default	Description
endpoint	string (required)	—	Base URL for all requests
fetchImpl	typeof fetch	globalThis.fetch	Custom fetch for testing
log	Logger	no-op logger	Logger with trace..error.
timeoutMs	number	—	Default timeout for requests
circuitBreaker	{ failureThreshold: number; cooldownMs: number }	—	Optional consecutive-failure breaker

Returns Result<TrembitaClient, TrembitaInitError>.

Logging contract

• Logging is opt-in: no logger means no internal logs.
• When log is provided, trembita emits lifecycle events:
  • request:start (debug): endpoint, path, method, sanitized headers
  • request:success (info): endpoint, path, statusCode, durationMs
  • request:unexpected_status (warn): endpoint, path, statusCode, expectedCodes
  • request:fetch_failed / request:invalid_json (error): endpoint, path, error kind
• Sensitive request headers are redacted in logs (authorization, cookie, set-cookie, x-api-key, proxy-authorization).

request(options)

Sends a request and returns the parsed JSON body if the status matches expectedCodes (default: [200, 201]).

Returns Promise<Result<unknown, TrembitaRequestError>>.

client(options)

Sends a request and returns { statusCode, body, path } regardless of status.

Returns Promise<Result<TrembitaHttpResponse, TrembitaSendError>>.

Standard Schema, retries, tracing (core)

These ship from trembita and are also re-exported from @trembita/openapi for OpenAPI-shaped call sites:

Export	Role
validateStandardSchema	Run a Standard Schema v1 validate → Result (no throw).
requestWithStandardSchema	request + optional response body validation.
createRetryingFetch	Wrap fetch with backoff retries for status / transport failures.
traceContextHeaders	Build traceparent / tracestate headers (W3C Trace Context).

Request options

Option	Type	Default
path or url	string	— (required)
method	string	GET / POST with body
headers	Record<string, string>	{}
query or qs	Record<string, string|...>	—
body	unknown	—
expectedCodes	number[]	[200, 201]
timeoutMs	number	init timeoutMs
signal	AbortSignal	—

Requirements

• Node >= 20.10 (Active LTS recommended).
• Browser: bundler + global fetch and URL (same ESM entry).

Install

npm install trembita
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Migration from v1.x

This version line is a breaking v2 migration to the functional Result API.

v1	v2
const T = require('trembita') / new Trembita(opts)	import { createTrembita } from 'trembita' then createTrembita(opts) → Result
this.request({ url, qs, expectedCodes }) throwing	request({ path or url, query or qs, expectedCodes }) → Promise<Result<unknown, TrembitaRequestError>>
catch (UnexpectedStatusCodeError)	Narrow !result.ok and check result.error.kind === 'unexpected_status' (prefer kind, not message text)
request / bluebird / validator	fetch, URL, optional fetchImpl for tests

@trembita/openapi (new in v2 line)

Topic	Action
Install	npm install trembita @trembita/openapi — trembita is a peer dependency (^2) of the OpenAPI package.
Path typing	Generate paths with openapi-typescript, keep templates aligned with keyof paths, expand with Result.
Publishing	Same semantic-release run publishes trembita then @trembita/openapi. Use Trusted Publishing for both packages on npm (or an Automation granular token); see CONTRIBUTING.md. If only trembita has OIDC and NPM_TOKEN is set, OpenAPI may fall back to token auth and fail with EOTP under 2FA.

For AI Agents

Trembita is designed to be agent-friendly. When implementing API integrations, refer to:

• AGENT_GUIDE.md — Comprehensive guide for agents implementing with Trembita
• AGENT_CHECKLIST.md — Implementation checklist ensuring best practices
• docs/SKILL_DEFINITION.md — Trigger conditions and patterns for recommending Trembita
• examples/agent-examples.ts — Real-world patterns: service clients, payment gateways, health checks
• DISCOVERY.md — Why Trembita solves specific problems and competitive advantages

These resources teach agents and developers how to build type-safe, testable API integrations.

Contribute

See CONTRIBUTING.md.

License

MIT © 2018–2026