DeepSeek Delegate MCP

A tiny local MCP server that exposes DeepSeek V4 to Codex as a single tool: call_deepseek_sub_agent.

It turns Codex into a hybrid agent: GPT Sol stays the architect (planning, reviewing, integrating) and DeepSeek V4 Flash does the cheap execution (boilerplate files, test-suite generation, bulk text transformation) at $0.14 per 1M input tokens.

How it works

┌────────────────────────┐   call_deepseek_sub_agent   ┌────────────────────────────┐
│  GPT Sol (Codex agent) │ ───────────────────────────▶ │  local MCP server (node)   │
│  plans / reviews /     │ ◀─────────────────────────── │  "deepseek-delegate"       │
│  integrates            │        output text          └─────────────┬──────────────┘
└────────────────────────┘                                          │ POST /responses
                                                                     ▼
                                                    DeepSeek API (api.deepseek.com)
                                                    deepseek-v4-flash / deepseek-v4-pro

Codex runs one model per session, so instead of switching providers mid-task you give Sol a delegation tool. Sol crafts a precise prompt, DeepSeek answers with plain text, and Sol reviews + applies the result. No file access is granted to DeepSeek — it only ever sees the exact prompt you send.

Features

• Single MCP tool: call_deepseek_sub_agent (prompt required; model, system, temperature, max_output_tokens, reasoning_effort optional)
• Uses DeepSeek's native Responses API
• Zero extra key setup if you already use DeepSeek's official Codex integration
• Works with Codex CLI, the ChatGPT desktop app, and the Codex IDE extension

Requirements

• Codex (CLI or desktop app)
• A DeepSeek API key from the DeepSeek Platform
• Node.js 18+

Quick start

1. Clone and install

git clone https://github.com/trixmix821/deepseek-delegate-mcp.git
cd deepseek-delegate-mcp
npm install

2. Register the MCP server

Add this to ~/.codex/config.toml (use the absolute path from step 1):

[mcp_servers.deepseek-delegate]
command = "node"
args = ["/absolute/path/to/deepseek-delegate-mcp/deepseek-mcp-server.mjs"]
env_vars = ["DEEPSEEK_API_KEY"]
tool_timeout_sec = 600
default_tools_approval_mode = "auto"

3. Provide your API key

The server looks for the key in this order:

1. DEEPSEEK_API_KEY environment variable
2. experimental_bearer_token under [model_providers.deepseek] in ~/.codex/config.toml (this is what DeepSeek's official Codex setup script writes — if you've run it, you're already done)

export DEEPSEEK_API_KEY=sk-...

4. Teach Sol to delegate

Append to ~/.codex/custom_instructions.md:

## Hybrid Architect: Sol (planner) + DeepSeek (executor)

You are the master architect (GPT Sol). You own the high-level plan, design,
and project structure. DeepSeek is your cheap execution layer.

For massive boilerplate files, extensive test-suite generation, bulk/repetitive
text transformation, or well-specified mechanical subtasks, invoke the
`call_deepseek_sub_agent` tool instead of doing the work in your own context.
Craft a precise, self-contained prompt: exact file paths, signatures, language,
framework, constraints, and expected output format. Never delegate open-ended
design decisions. Review DeepSeek's output, fix logic/interface mismatches, then
integrate. If you are already running as a DeepSeek model, do not delegate.

5. Verify

node test-deepseek.mjs "Reply with exactly: OK"

Expected output: the model replies OK, and a usage line ([deepseek-delegate] model=... input_tokens=... output_tokens=...) is printed to stderr.

Then restart Codex so it loads the new MCP server (in the TUI, /mcp shows active servers), and ask something like: "delegate the test-suite boilerplate to DeepSeek."

Tool reference

call_deepseek_sub_agent

Parameter	Type	Required	Default	Description
prompt	string	yes	—	The exact coding instruction or context to process
model	string	no	deepseek-v4-flash	deepseek-v4-flash or deepseek-v4-pro
system	string	no	—	Optional system prompt for the sub-agent
temperature	number	no	—	0.0–2.0 (no effect in thinking mode)
max_output_tokens	number	no	8192	Maximum output tokens
reasoning_effort	string	no	—	low, high, or max
thinking	boolean	no	off	Force thinking mode on/off

Which model? deepseek-v4-flash is the default and right for nearly all delegated work (boilerplate, tests, transformations). Escalate to deepseek-v4-pro only when a single small task genuinely needs stronger reasoning — it costs ~3x more.

Configuration

Environment variables (all optional):

Variable	Default	Description
DEEPSEEK_API_KEY	—	DeepSeek API key (falls back to your Codex config)
DEEPSEEK_MODEL	deepseek-v4-flash	Default model for the tool
DEEPSEEK_BASE_URL	https://api.deepseek.com	API base URL
DEEPSEEK_WIRE_API	responses	responses or chat (OpenAI-style chat completions)
DEEPSEEK_THINKING	disabled	enabled or disabled thinking mode default (disabled = fast/cheap)
DEEPSEEK_MAX_PROMPT_CHARS	30000	Reject prompts larger than this to prevent giant-payload delegation

Costs

DeepSeek V4 pricing (per 1M tokens, source):

Model	Input (cache miss)	Input (cache hit)	Output
deepseek-v4-flash	$0.14	$0.0028	$0.28
deepseek-v4-pro	$0.435	$0.003625	$0.87

Context window is 1M tokens; max output is 384K.

Security notes

• The server only calls the DeepSeek API. It never reads or writes your files, and DeepSeek only sees the text you put in the prompt.
• DeepSeek's official setup stores your key in ~/.codex/config.toml in plaintext. Prefer export DEEPSEEK_API_KEY=... and keep the token out of the file.
• default_tools_approval_mode = "auto" lets Sol call the tool without a prompt; change it to prompt if you want to approve every delegation.

Limitations

• The tool only receives the prompt text — it has no access to your repository, so delegated prompts must be self-contained.
• Delegation is only worth it for SMALL, mechanical, self-contained tasks. Prompts over 30,000 chars are rejected (configurable via DEEPSEEK_MAX_PROMPT_CHARS) — split them into smaller subtasks instead.
• Thinking mode is off by default for speed; enable it via the thinking tool parameter only when the task genuinely needs reasoning.
• Delegation is a judgment call by the agent. Explicitly asking for it ("delegate X to DeepSeek") makes it deterministic.
• If your session is already running on DeepSeek, delegation is redundant.

License

MIT