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Enrico Testori
Enrico Testori

Posted on • Originally published at hypertesto.me

Adding a custom DeepSeek model in Junie CLI (No YAML demons required)

#llm #cli #productivity

I switched my Junie CLI default model to DeepSeek last month. The reason wasn't philosophical: Claude and GPT are great, but they cost real money when you're hammering a CLI for hours. DeepSeek is cheaper. Sometimes the best technical decision is the one your wallet makes for you.

The switch itself was anticlimactic. There's no junie model add wizard, no guided setup, and the --help output mentions custom models only in passing with a --model flag that reads like an afterthought. What you actually do is drop a JSON file into ~/.junie/models/ and… that's it. Junie picks it up.

This post documents that process: adding deepseek-v4-pro to Junie CLI, using the actual config format running on my machine right now.1

Why bother?

Before we touch any config, let's answer the obvious: why not just use the built-in providers?

Because in real life we optimize for different things at different times:

You want… So you reach for…
Latency minimization a flash/fast variant
Deep refactors with context a large-context model
Cost control on long sessions a cheaper provider
Provider redundancy a backup endpoint
Experimentation whatever just dropped on HuggingFace

If your tooling lets you swap models cleanly, you gain operational sanity. And operational sanity is underrated.

Prerequisites

  1. Junie CLI installed. You should already have junie on your PATH. Verify: 
   junie --help
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  1. A DeepSeek API key. Get one from platform.deepseek.com. You'll need to top up credits.

  2. Basic JSON literacy. No YAML, no TOML, no arcane DSL. Just one JSON file. You've got this.

How Junie CLI discovers custom models

Junie looks for model definitions in two default locations:

  • ~/.junie/models/: global, available to all projects
  • <project>/.junie/models/: per-project overrides

Each model is a single .json file. The filename becomes the model's identifier within Junie. So ~/.junie/models/deepseek.json registers a model called… deepseek. Creative, I know.

You can also point Junie at additional directories with --model-location <path> if you prefer to keep your model configs in a dotfiles repo or shared volume.

Step 1 — Create the model JSON

Create ~/.junie/models/deepseek.json (or <project>/.junie/models/deepseek.json if you want it scoped to a single codebase):

{
  "id": "deepseek-v4-pro",
  "baseUrl": "https://api.deepseek.com/chat/completions",
  "apiType": "OpenAICompletion",
  "apiKey": "sk-your-deepseek-api-key-here",
  "temperature": 0,
  "primaryModel": {
    "id": "deepseek-v4-pro"
  },
  "fasterModel": {
    "id": "deepseek-v4-flash"
  }
}
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Let's unpack what each field does:

Field Purpose
id The primary model identifier. Junie displays this in the model picker and passes it in API requests.
baseUrl The endpoint Junie POSTs to. DeepSeek's API is OpenAI-compatible, so we point it at their chat/completions endpoint.
apiType Tells Junie which request/response format to use. "OpenAICompletion" covers OpenAI, DeepSeek, and most compatible providers.
apiKey Your API key. Yes, it's plaintext in a JSON file. We'll talk about this.
temperature Controls response randomness. 0 means deterministic; bump it to 0.3–0.7 for more creative output.
primaryModel.id The model ID sent in the API request body. This must match the DeepSeek model name exactly.
fasterModel (Optional) A lighter/faster model for quick tasks like inline autocomplete or summarization.

A stern word about apiKey

Yeah, it's sitting there in plaintext. I know. No, Junie doesn't currently read it from an environment variable for custom models2. Your options:

  • Set restrictive file permissions: chmod 600 ~/.junie/models/deepseek.json. At least other users on the system can't read it.
  • Use a LiteLLM proxy as middleware (see the LiteLLM section below): this keeps the key out of Junie's config entirely.
  • Accept it and don't commit the file to a public dotfiles repo. You're an adult.

For what it's worth, Junie stores the key in your home directory, which on a single-user development machine is about as secure as any other dotfile with secrets in it. Not ideal, but not the end of the world either3.

Step 2 — Use the model

Once the JSON file is in place, you have three ways to invoke it:

  • CLI flag (one-off) 
  junie --model custom:deepseek "Explain this function."
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This will start junie in interactive mode using the custom model defined previously in json configuration.

  • Interactive mode

Launch Junie interactively, then pick the model from the selector (usually /model or the equivalent model-switching shortcut):

  junie
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Your custom deepseek model should appear in the list alongside the built-in providers.

Settings override (persistent default)

Edit ~/.junie/settings.json and add or edit:

{
  "modelForLaunch": "custom:deepseek",
}
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Now every session starts with DeepSeek unless you override with --model.

Step 3 — Verify it works

Before trusting it with a 400-line refactor, run a quick sanity check:

junie --model custom:deepseek "Say hello and confirm which model you're running on."
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If the response comes back coherent and the logs show deepseek-v4-pro, you're in business. If you get an auth error, double-check:

  • The API key is correct and has credits
  • The baseUrl ends with /chat/completions (no trailing slash weirdness)
  • The primaryModel.id matches exactly what DeepSeek expects

The bottom line

Junie CLI's custom model system is refreshingly straightforward: drop a JSON file in a directory, and you're done. No YAML anchors, no multi-file inheritance chains, no environment-variable indirection puzzles. Just a flat config that tells the CLI where to send requests and which model ID to use.

Is the plaintext API key ideal? No. But with file permissions and/or a LiteLLM proxy, you can mitigate the concern without adding much friction. For single user dev-machines it's a worth tradeoff.

Now go wire up your DeepSeek model and tell it to write you some code. Or a haiku about YAML. Your call.

Thanks for reading!

  1. If you're looking for the accompanying Italian version of this post… there isn't one. Some topics just work better in English, and CLI config files are definitely in that camp. "Drop un JSON nella cartella models" doesn't quite hit the same way. ↩

  2. If you're reading this from the future and Junie does support apiKeyEnv or similar: congratulations, the timeline is better than mine. Please update this post. ↩

  3. "Not the end of the world" is the security posture equivalent of "it compiles, ship it." Take appropriate precautions. ↩

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