@ferscloud/fers-calculation

High-performance structural engineering FEM solver compiled from Rust to WebAssembly. Runs entirely in the browser — no server round-trip per calculation.

Installation

npm install @ferscloud/fers-calculation

Quick start — free tier (up to 100 members)

import init, { calculate_from_json } from "@ferscloud/fers-calculation";

await init(); // load the WASM module once

const result = calculate_from_json(JSON.stringify(myModel));
const data = JSON.parse(result);

No API key required. Works for any model with up to 100 members.

Authenticated tier — Pro (up to 10 000 members)

Pro limits are unlocked by passing a short-lived signed token issued by the FERS Cloud server. The token is verified inside the WASM using an Ed25519 public key baked into the binary — it cannot be forged.

How it works

Your server  →  POST https://ferscloud.com/api/solver/token  →  signed 30-min token
                (X-API-Key: <your-api-key>)

Browser  →  calculate_from_json_with_token(model, token)  →  Pro limits unlocked

1. Get an API key

Log in at ferscloud.com, go to Profile → API Keys, and create a key. Store it as an environment variable on your server — never in browser code.

2. Backend: fetch a solve token

Your server fetches and caches the token. Example for a Next.js API route:

// pages/api/solve-token.ts
const FERS_API_KEY = process.env.FERS_API_KEY!;

let cached: { token: string; expiresAt: number } | null = null;

export default async function handler(req, res) {
  const now = Date.now();

  // Re-use if more than 5 minutes remain
  if (cached && cached.expiresAt - now > 5 * 60 * 1000) {
    return res.json({ token: cached.token });
  }

  const resp = await fetch("https://ferscloud.com/api/solver/token", {
    method: "POST",
    headers: { "X-API-Key": FERS_API_KEY },
  });

  if (!resp.ok) return res.status(502).json({ error: "Token fetch failed" });

  const { token, expiresAt } = await resp.json();
  cached = { token, expiresAt: new Date(expiresAt).getTime() };
  return res.json({ token });
}

Same pattern works for Express, Deno, Bun, Cloudflare Workers, or any server-side runtime.

3. Frontend: call the solver with the token

import init, { calculate_from_json_with_token } from "@ferscloud/fers-calculation";

await init();

const { token } = await fetch("/api/solve-token").then(r => r.json());

const result = calculate_from_json_with_token(JSON.stringify(myModel), token);
const data = JSON.parse(result);

If the token is missing, expired, or invalid, the solver falls back to the free 100-member limit — it never throws.

Tier comparison

| Feature | Free | Pro | |---|---|---| | Max members | 100 | 10 000 | | WASM function | calculate_from_json | calculate_from_json_with_token | | Requires token | No | Yes | | Token TTL | — | 30 minutes |

Security note

Keep your FERS_API_KEY server-side only. The solve token it fetches is safe to pass to the browser — it is short-lived and cryptographically signed. Only FERS Cloud can issue valid tokens; the browser WASM can only verify them.

Links

• Full documentation & getting started
• FERS Cloud
• FERS_core Python package