OpenAI-Compatible API

Writingmate exposes an OpenAI-compatible API so you can use your Writingmate workspace from external tools and SDKs.

Requests made through this API are billed against your current Writingmate workspace using the same token-to-message counting logic as Writingmate chat.

Before you start

1. Open Profile Settings in Writingmate.
2. Go to API Keys.
3. Create a Writingmate Developer Key.
4. Copy the key when it is shown. The full value is only displayed once.

Base URL

https://writingmate.ai/api/openai/v1

Authentication

Use your Writingmate developer key as a Bearer token:

Authorization: Bearer YOUR_WRITINGMATE_DEVELOPER_KEY

Supported endpoints

Writingmate currently supports these OpenAI-compatible endpoints:

• GET /models
• GET /models/{id}
• POST /chat/completions
• POST /completions
• POST /responses
• POST /audio/transcriptions

Model names

Use Writingmate model slugs such as:

• openai/gpt-5-mini
• openai/gpt-5
• anthropic/claude-sonnet-4.5
• google/gemini-2.5-pro

Fetch the live list from:

curl https://writingmate.ai/api/openai/v1/models \
  -H "Authorization: Bearer YOUR_WRITINGMATE_DEVELOPER_KEY"

Chat Completions example

curl https://writingmate.ai/api/openai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_WRITINGMATE_DEVELOPER_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5-mini",
    "messages": [
      { "role": "system", "content": "Be concise." },
      { "role": "user", "content": "Summarize Writingmate in one sentence." }
    ]
  }'

Responses API example

curl https://writingmate.ai/api/openai/v1/responses \
  -H "Authorization: Bearer YOUR_WRITINGMATE_DEVELOPER_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5-mini",
    "input": "Write a short launch announcement for a new developer API."
  }'

OpenAI SDK example

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.WRITINGMATE_API_KEY,
  baseURL: "https://writingmate.ai/api/openai/v1",
});

const response = await client.responses.create({
  model: "openai/gpt-5-mini",
  input: "Say hello from Writingmate.",
});

console.log(response.output_text);

OpenCode and other OpenAI-compatible CLIs

If your client supports a custom OpenAI base URL, point it to Writingmate:

export OPENAI_API_KEY=YOUR_WRITINGMATE_DEVELOPER_KEY
export OPENAI_BASE_URL=https://writingmate.ai/api/openai/v1

Then choose a Writingmate model slug, for example openai/gpt-5-mini.

Most OpenAI-compatible CLIs and libraries only need:

• a Bearer API key
• a custom base URL
• a model name returned by /models

Workspace selection

By default, the API uses your current workspace.

If your client lets you send custom headers, you can target a specific workspace with:

x-writingmate-workspace: WORKSPACE_ID

The workspace must belong to the authenticated user.

Usage and limits

Writingmate applies the same access rules and usage accounting as the app:

• model availability still depends on your Writingmate plan
• daily and AppSumo limits still apply
• BYOK OpenRouter behavior still applies if you configured your own OpenRouter key
• cached prompt tokens are discounted the same way they are in Writingmate chat

Tool calling

/chat/completions and /responses support OpenAI-style function tools for single-step tool calling.

Notes

• This API is OpenAI-compatible, not byte-for-byte identical to every OpenAI feature.
• Use /models to discover the currently supported model list.
• For audio transcription details, see the separate transcription documentation.