DeepSeek API in TypeScript: secure integration and honest model evaluation for code

For months I was convinced that integrating a new model into a TypeScript pipeline was the hard part. Then I realized it never was. The hard part is deciding whether that model is actually worth it for what you need — without buying the hype or trashing it because Twitter moved on. I learned that lesson again with DeepSeek.

My thesis before starting: DeepSeek's API is compatible with the OpenAI SDK, which makes integration almost trivial in any existing TypeScript pipeline. The real differentiator isn't the plumbing — it's the model. DeepSeek-Coder is competitive for code tasks, but the decision criterion depends on your specific use case, not on Twitter enthusiasm.

What the official docs say — and what they don't

The official DeepSeek documentation has two facts that completely change the integration conversation:

OpenAI SDK compatibility: DeepSeek exposes its API under the same message format as OpenAI. That means if you're already using the openai npm package in a TypeScript pipeline, you can point it at DeepSeek's base URL with minimal changes.

Available models: As of this post, the main models are deepseek-chat (general purpose) and deepseek-coder (code-focused). The docs list the base endpoint as https://api.deepseek.com.

What the documentation doesn't say: independent benchmarks, real production latency comparisons, or SLA guarantees. That's your own work — or someone willing to run the experiment under real load. I'm not going to make up those numbers here.

How to integrate in TypeScript without exposing the API key

Core decision: the DeepSeek API key, like any LLM provider credential, cannot live on the client. Ever. In Next.js App Router that has a concrete answer: the logic that calls the API lives in a Route Handler (server-side), and the key travels exclusively via server environment variable.

Step 1: environment variable in .env.local

# .env.local — NEVER commit this file
DEEPSEEK_API_KEY=sk-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Add it to .gitignore if it isn't already. On Railway, Vercel, or any deploy platform, you configure the variable from the dashboard — never from the repository.

Step 2: TypeScript client with OpenAI SDK compatibility

// lib/deepseek-client.ts
import OpenAI from "openai";

// Instance pointing to DeepSeek's endpoint
// Compatible with openai@^4 — same type contract
const deepseek = new OpenAI({
  apiKey: process.env.DEEPSEEK_API_KEY, // only available server-side
  baseURL: "https://api.deepseek.com",
});

export default deepseek;

The key is in baseURL: the OpenAI SDK accepts endpoint override, and DeepSeek respects the same message contract. You don't need a proprietary SDK.

Step 3: Route Handler in Next.js App Router

// app/api/code-review/route.ts
import { NextRequest, NextResponse } from "next/server";
import deepseek from "@/lib/deepseek-client";

export async function POST(req: NextRequest) {
  const { code } = await req.json();

  // Minimal validation before calling the model
  if (!code || typeof code !== "string" || code.length > 8000) {
    return NextResponse.json({ error: "Invalid payload" }, { status: 400 });
  }

  const completion = await deepseek.chat.completions.create({
    model: "deepseek-coder", // code-focused model
    messages: [
      {
        role: "system",
        content: "Review the code and flag concrete issues with justification.",
      },
      { role: "user", content: code },
    ],
    max_tokens: 1024,
  });

  return NextResponse.json({
    review: completion.choices[0]?.message?.content ?? "",
  });
}

The client never sees the key. The browser calls /api/code-review; the Route Handler calls DeepSeek. That's the pattern.

Where people get it wrong — and what it costs

There are three common mistakes that show up in quick LLM API integrations. I'm listing them as practical criteria, because the patterns are reproducible even if the specific experience is generic:

Mistake 1: exposing the key on the client The typical case is a dev who copies the documentation snippet directly into a React component. process.env.DEEPSEEK_API_KEY on the client is undefined in Next.js by default — but if someone prefixes the variable with NEXT_PUBLIC_, it gets exposed in the browser bundle. Cost: the key is accessible in DevTools and in any scraper that inspects the public JS.

Mistake 2: treating deepseek-chat and deepseek-coder as synonyms They're different models with different biases. deepseek-coder was trained specifically for code generation and review tasks; deepseek-chat is more general. Using the wrong model doesn't break the API — it breaks the quality of the response. The documentation distinguishes them explicitly.

Mistake 3: assuming OpenAI SDK compatibility is total The compatibility is at the message format and response structure level. It doesn't mean DeepSeek supports every OpenAI API feature: function calling, embeddings, fine-tuning, and advanced tooling may have differences or limitations. Before assuming full parity, check the DeepSeek documentation for the specific feature you need.

Decision matrix: DeepSeek-Coder vs Claude for code tasks

This is the part where most posts hand you a winner and call it done. I'm not going to do that — because the honest answer depends on variables I can't measure for you.

What I can give you is the decision framework:

When it's worth trying DeepSeek-Coder first:

• The pipeline is exclusively code generation or review
• API cost is a relevant variable in the design
• You're already on the OpenAI SDK and want minimal friction to evaluate

When to stick with Claude:

• You need multi-step reasoning or very long context
• Model behavior predictability matters more than cost
• The pipeline mixes code tasks with general reasoning or analysis

What you can't decide without your own experiment: perceived response speed in production, quality on your specific code domain, and behavior under load. That data doesn't exist in any post — it exists in your own logs.

What this guide can't conclude

Being honest here is part of the job:

• No first-party benchmarks: I didn't run systematic comparisons between DeepSeek-Coder and Claude against real use cases. The public benchmarks circulating out there have different methodologies and aren't always reproducible.
• DeepSeek's documentation can change: it's an actively growing platform. What's available today may change. Always check https://platform.deepseek.com/api-docs/ before making architecture decisions.
• OpenAI SDK compatibility is not a parity guarantee: it's an entry point, not a complete contract. Test the specific feature you need.
• Relative API costs fluctuate: don't anchor architecture decisions to pricing numbers that change every quarter.

FAQ — Common questions about DeepSeek API in TypeScript

Do I need a special SDK to use DeepSeek in TypeScript? No. You can use the official openai npm package pointing baseURL at https://api.deepseek.com. DeepSeek respects the same message format, so the OpenAI SDK's TypeScript types work without modifications.

What's the real difference between deepseek-chat and deepseek-coder? According to the official documentation, deepseek-coder was trained specifically for code tasks: generation, explanation, debugging, and review. deepseek-chat is the general-purpose model. For a code-focused pipeline, deepseek-coder is the logical starting point.

How do I protect the API key in a Next.js project? The key lives in .env.local (never in the repository) and is used exclusively in server-side code: Route Handlers or Server Actions. Never prefix the variable with NEXT_PUBLIC_ — that exposes it in the browser bundle. In production, configure it from your deploy platform's dashboard.

Can I use DeepSeek and Claude in the same pipeline? Yes, and it's a reasonable pattern: use DeepSeek-Coder for mechanical code tasks (boilerplate generation, conversions, snippets) and Claude for more complex reasoning or long context. The router between models is logic you write yourself. This connects to the same design decision that comes up in rate limiting in web applications: deciding which layer you protect and with what tool.

Does OpenAI SDK compatibility guarantee all features will work the same? No. Compatibility is at the basic chat completions level. Features like function calling, embeddings, batch API, or fine-tuning may have differences or simply not be available in DeepSeek. Before assuming parity, verify the specific feature you need in the official documentation.

Does it make sense to use DeepSeek in a pipeline that already uses Claude or GPT-4? Depends on the case. If API cost is relevant and the tasks are mechanical (repetitive code generation, formatting, short snippets), it's worth evaluating. If the pipeline depends on multi-step reasoning or very long context, the switch may degrade response quality. The honest decision comes from running the experiment in your own domain, not from general benchmarks.

The real decision, no decoration

Integrating DeepSeek in TypeScript is easy — intentionally easy. The OpenAI SDK compatibility is a product decision that brings adoption friction down to nearly zero. That's a real advantage and it deserves acknowledgment.

What isn't easy is the model decision. And here my position is clear: I'm not buying anyone's claim that DeepSeek-Coder is better than Claude for code "in general" — because "in general" doesn't exist in production. What exists is the specific domain, the type of task, the token volume, and the project budget.

What I do accept as a starting point: if you already have a pipeline on the OpenAI SDK and want to evaluate DeepSeek-Coder, the cost of the test is minimal. Change the baseURL, change the model, run the same set of prompts you already have, and look at the results. That's the only honest way to compare.

Twitter hype doesn't replace that experiment. Neither do I.

If pipeline architecture interests you, the post on Node.js and the event loop has useful context on how to think about the runtime behind these integrations. And if you're thinking about how to protect these endpoints before exposing them, the rate limiting post is the next step.

Original source:

• DeepSeek API Documentation: https://platform.deepseek.com/api-docs/