tls-client-node is a source-available Node.js client for bogdanfinn/tls-client. It uses managed tls-client-api mode by default for predictable async concurrency, keeps lifecycle control explicit through TLSClient and Session, and can also run through direct shared-library loading when native mode is explicitly selected.

Why tls-client-node

| Focus | What you get | | --- | --- | | Managed-first local runtime | Uses the tls-client-api sidecar process by default for more predictable concurrent async behavior. | | Explicit lifecycle | TLSClient and Session keep ownership obvious, instead of hiding everything behind global init and destroy calls. | | Upstream alignment | Custom TLS payloads and profile identifiers are kept close to Bogdan Finn's tls-client contract. | | Migration practicality | Common node-tls-client aliases such as ja3string, timeout, hostOverride, and randomTlsExtensionOrder are supported. | | Modern package surface | Published npm package with strict TypeScript types, named ESM imports, and CommonJS require support. |

Highlights

• Clean named ESM imports and CommonJS require support.
• Default local runtime uses managed tls-client-api.
• Native mode is available through runtimeMode: "native".
• Session-oriented API with explicit client and session control.
• Strict custom TLS handling with no silent fallback to stock client identifiers.

Installation

npm install tls-client-node
# or
yarn add tls-client-node
# or
pnpm add tls-client-node

During postinstall, the package tries to download the matching upstream shared library for the current platform. If that step is skipped or fails, the required local asset is downloaded lazily on first startup.

Environment variables:

• TLS_CLIENT_SKIP_DOWNLOAD=1 disables install-time downloads.
• TLS_CLIENT_VERSION=1.14.0 pins the upstream asset version.
• TLS_CLIENT_API_VERSION=1.14.0 is also recognized as an alias for TLS_CLIENT_VERSION.
• TLS_CLIENT_RUNTIME_SLOTS=128 caps how many managed tls-client-api runtimes can run at once on a host (default 128). The per-client runtimeSlots option overrides it. See Runtime Modes.

Imports

ESM named imports work directly:

import {
  ClientIdentifier,
  Emulation,
  MultipartForm,
  TLSClient,
  createMultipartForm,
} from "tls-client-node";

const client = new TLSClient();
const session = client.session({
  clientIdentifier: Emulation.chrome_136,
});

CommonJS is supported too:

const { ClientIdentifier, Emulation, MultipartForm, TLSClient, createMultipartForm } = require("tls-client-node");

Quick Start

import {
  ClientIdentifier,
  TLSClient,
} from "tls-client-node";

async function main() {
  const client = new TLSClient();
  const session = client.session({
    clientIdentifier: ClientIdentifier.chrome_136,
  });

  const response = await session.get("https://tls.peet.ws/api/all");
  console.log(response.status, await response.text());

  await session.close();
  await client.stop();
}

main().catch(console.error);

High-Level Client

import { ClientIdentifier, TLSClient } from "tls-client-node";

const client = new TLSClient();

const session = client.session({
  clientIdentifier: ClientIdentifier.chrome_136,
  timeoutSeconds: 30,
  headers: {
    "user-agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/136.0.0.0 Safari/537.36",
    accept: "*/*",
    "accept-language": "en-US,en;q=0.9",
    "accept-encoding": "gzip, deflate, br",
  },
});

const response = await session.get("https://tls.peet.ws/api/all");
console.log(response.status, response.usedProtocol);

await session.close();
await client.stop();

One-Off Requests

import { ClientIdentifier, fetch } from "tls-client-node";

const response = await fetch("https://example.com", {
  clientIdentifier: ClientIdentifier.chrome_136,
  headers: {
    accept: "text/html",
  },
});

console.log(await response.text());

Multipart Form Uploads

import { MultipartForm, TLSClient, createMultipartForm } from "tls-client-node";

const client = new TLSClient();
const form = createMultipartForm({
  title: "example",
  file: {
    data: "hello world",
    filename: "hello.txt",
    contentType: "text/plain",
  },
});

const builder = new MultipartForm()
  .append("kind", "builder")
  .appendJson("meta", { ok: true });

const response = await client.request("https://example.com/upload", {
  method: "POST",
  body: form,
});

console.log(response.status);

await client.request("https://example.com/upload-builder", {
  method: "POST",
  body: builder,
});

await client.stop();

Redirect Ergonomics

import { TLSClient } from "tls-client-node";

const client = new TLSClient();
const session = client.session({
  redirect: "follow",
});

await session.get("https://example.com/start", {
  redirect: "manual",
});

await client.stop();

redirect is a higher-level alias for followRedirects.

• redirect: "follow" maps to followRedirects: true
• redirect: "manual" maps to followRedirects: false
• redirect: true and redirect: false are also accepted

Runtime Modes

Default local mode is managed tls-client-api.

Use native mode only when you explicitly want direct shared-library loading:

import { TLSClient } from "tls-client-node";

const client = new TLSClient({
  runtimeMode: "native",
});

If you already host tls-client-api yourself, use remote mode:

import { TLSClient } from "tls-client-node";

const client = new TLSClient({
  baseUrl: "http://127.0.0.1:8080",
  apiKey: "my-auth-key-1",
});

Managed runtime slots

In managed mode each started TLSClient claims an isolated runtime slot — its own runtime directory, lock file, and tls-client-api child process — so multiple clients (and multiple OS processes) never collide on the same files or ports. A single runtime serves many concurrent sessions and requests, so you normally need one slot per long-lived process, not one per request.

Slots live under the runtime cache, keyed by upstream version:

| Platform | Location | | --- | --- | | Linux | ${XDG_CACHE_HOME:-~/.cache}/tls-client-node/runtime/<version>/slot-N/ | | macOS | ~/Library/Caches/tls-client-node/runtime/<version>/slot-N/ | | Windows | single managed runtime under %LOCALAPPDATA%\tls-client-node\runtime (the slot pool applies only when you set runtimeDir) |

The slot ceiling is resolved as runtimeSlots option → TLS_CLIENT_RUNTIME_SLOTS env → default 128:

const client = new TLSClient({
  runtimeSlots: 256, // overrides TLS_CLIENT_RUNTIME_SLOTS and the default
});

The cap is a ceiling, not a reservation: slots are spawned only as they are claimed, so low-concurrency apps pay nothing for a high cap. Raise it only if you genuinely run that many concurrent managed runtimes on one host; each slot is a full native process with its own memory, file handles, and port. Invalid values (non-integers, zero, or negatives) fall back to the next source in the chain.

Reuse one client instead of creating a new one per request — and always release the slot when done:

const client = new TLSClient();
try {
  const session = client.session();
  // ...many concurrent requests share this one runtime slot...
} finally {
  await client.stop(); // releases the slot and stops the child process
}

The top-level fetch() helper spins up an isolated temporary client (one slot) per call when you do not pass an explicit client or session. For hot paths, pass a shared client.

Troubleshooting ERR_RUNTIME_SLOT_UNAVAILABLE

Unable to allocate a tls-client runtime slot after checking N slots means every slot is taken. Common causes:

• Too many concurrent runtimes — more started clients (or separate processes) than the slot cap. Reuse a shared client, or raise TLS_CLIENT_RUNTIME_SLOTS.
• Leaked locks — a runtime was force-killed (SIGKILL, kill -9, abrupt container stop) before client.stop() ran, leaving a stale .lock behind. Stale locks are reclaimed automatically only when the recorded PID is no longer alive, so on busy hosts where PIDs get recycled a dead owner can keep a slot pinned.

To clear stale slots when no runtimes should be active:

# Linux/macOS
pkill -f tls-client-api
rm -f ~/.cache/tls-client-node/runtime/*/slot-*/.lock           # Linux
rm -f ~/Library/Caches/tls-client-node/runtime/*/slot-*/.lock   # macOS

Calling await client.stop() (ideally in a finally, and on SIGINT/SIGTERM handlers) prevents leaks in the first place.

Custom TLS

import { TLSClient } from "tls-client-node";

const client = new TLSClient();

const response = await client.request("https://example.com/", {
  proxyUrl: "http://user:[email protected]:5959",
  followRedirects: true,
  headers: {
    "user-agent": "Mozilla/5.0 (Linux; Android 14; Pixel 8) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/136.0.0.0 Mobile Safari/537.36",
    accept: "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
    "accept-language": "en-US,en;q=0.9",
    "accept-encoding": "gzip, deflate, br",
  },
  customTlsClient: {
    ja3String: "771,2570-4865-4866-4867-49195-49199-49196-49200-52393-52392-49171-49172-156-157-47-53,2570-0-23-65281-10-11-35-16-5-13-18-51-45-43-27-17513-2570-21,2570-29-23-24,0",
    h2Settings: {
      HEADER_TABLE_SIZE: 65536,
      MAX_CONCURRENT_STREAMS: 1000,
      INITIAL_WINDOW_SIZE: 6291456,
      MAX_HEADER_LIST_SIZE: 262144,
    },
    h2SettingsOrder: [
      "HEADER_TABLE_SIZE",
      "MAX_CONCURRENT_STREAMS",
      "INITIAL_WINDOW_SIZE",
      "MAX_HEADER_LIST_SIZE",
    ],
    supportedSignatureAlgorithms: [
      "ECDSAWithP256AndSHA256",
      "PSSWithSHA256",
      "PKCS1WithSHA256",
      "ECDSAWithP384AndSHA384",
      "PSSWithSHA384",
      "PKCS1WithSHA384",
      "PSSWithSHA512",
      "PKCS1WithSHA512",
    ],
    supportedVersions: ["GREASE", "1.3", "1.2"],
    keyShareCurves: ["GREASE", "X25519"],
    certCompressionAlgos: ["brotli"],
    pseudoHeaderOrder: [":method", ":authority", ":scheme", ":path"],
    connectionFlow: 15663105,
    headerOrder: ["accept", "user-agent", "accept-encoding", "accept-language"],
    priorityFrames: [
      {
        streamID: 1,
        priorityParam: {
          streamDep: 1,
          exclusive: true,
          weight: 1,
        },
      },
    ],
    headerPriority: {
      streamDep: 1,
      exclusive: true,
      weight: 1,
    },
    alpnProtocols: ["h2", "http/1.1"],
    alpsProtocols: ["h2"],
  },
  headerOrder: [":method", ":authority", ":scheme", ":path"],
});

Notes

• Primary interface: create a TLSClient, create one or more Session instances, and stop the client when finished.
• Each Session keeps a tough-cookie jar in sync with request and response cookies. You can inspect URL cookies with session.cookies(url) or serialize the jar with session.exportCookies().
• Emulation is exported as a higher-level alias for ClientIdentifier, so Emulation.chrome_136 and ClientIdentifier.chrome_136 are equivalent.
• Binary responses are returned as a data URL when byteResponse: true is enabled, matching upstream behavior.
• FormData, MultipartForm, and createMultipartForm() can all be used for multipart uploads, with the generated boundary preserved in the content-type header.
• redirect is a higher-level alias over followRedirects; it improves call-site clarity without changing upstream redirect semantics.
• WebSocket upgrade and frame APIs are not currently implemented in this wrapper.
• New upstream client identifiers can be passed as plain strings even before this package adds them to ClientIdentifier.
• Custom TLS requests remain custom-only. Rejections such as tls: illegal parameter or unknown ClientHelloID: Custom-1 throw ERR_CUSTOM_TLS_REJECTED instead of falling back silently.
• If certCompressionAlgo is provided, it is normalized to the upstream certCompressionAlgos field before the request is sent.
• new TLSClient() is the primary lifecycle model. The top-level fetch() helper uses an isolated temporary client when you do not pass an explicit client or session.

License

This project is distributed under Apache License 2.0 with Commons Clause.

• You can use, modify, embed, and redistribute the library under the public license terms.
• You cannot sell the library itself, or sell a product or service whose value derives entirely or substantially from tls-client-node, without separate permission.
• Upstream runtime components downloaded by this package are subject to their own licenses and notices. See NOTICE.

This is source-available, not OSI open source.

Acknowledgement

This product includes software developed by Bogdan Finn and contributors via bogdanfinn/tls-client and bogdanfinn/tls-client-api.