# buildBasePrompt()

`buildBasePrompt()` builds the shared base system prompt for a coding agent — the behavioral instructions that make the agent a good coding assistant. It takes a `PromptContext` describing the current environment (project, platform, git branch, mode, model) and returns the prompt as a string.

Product-specific strings are parameterized through `productName`, `coAuthorName`, and `coAuthorEmail`, so you can rebrand the prompt and commit trailer without forking it. They default to `"Mastra Code"` / `"noreply@mastra.ai"`, so existing callers keep identical output.

Use this with [`createCodingAgent()`](https://mastra.ai/reference/coding-agent/create-coding-agent) when you build dynamic instructions for the agent.

## Usage example

Build the base prompt from a `PromptContext`:

```typescript
import { buildBasePrompt } from '@mastra/core/coding-agent'

const prompt = buildBasePrompt({
  projectPath: process.cwd(),
  projectName: 'my-app',
  gitBranch: 'main',
  platform: process.platform,
  date: new Date().toDateString(),
  mode: 'build',
  modelId: 'openai/gpt-5',
  toolGuidance: '',
})
```

To rebrand the prompt, pass the product and co-author fields:

```typescript
const prompt = buildBasePrompt({
  // ...environment fields
  productName: 'Acme Coder',
  coAuthorName: 'Acme Bot',
  coAuthorEmail: 'bot@acme.dev',
})
```

## Parameters

`buildBasePrompt()` takes a single `PromptContext` object.

**projectPath** (`string`): Absolute path to the project root.

**projectName** (`string`): Display name of the project.

**gitBranch** (`string`): Current git branch, if the project is a git repository.

**platform** (`string`): Operating system platform (for example, the value of process.platform).

**commonBinaries** (`{ name: string; path: string | null }[]`): Common binaries detected on the system, each with a name and resolved path (or null when not found).

**date** (`string`): Current date string injected into the prompt.

**mode** (`string`): Active agent mode (for example, "build" or "plan").

**modelId** (`string`): Identifier of the active model, included in the commit Co-Authored-By line when provided.

**activePlan** (`{ title: string; plan: string; approvedAt: string } | null`): The currently approved plan, if any.

**toolGuidance** (`string`): Tool-usage guidance section appended to the prompt.

**productName** (`string`): Display name used in the prompt header. (Default: `Mastra Code`)

**coAuthorName** (`string`): Name used in the commit Co-Authored-By line. (Default: `Mastra Code`)

**coAuthorEmail** (`string`): Email used in the commit Co-Authored-By line. (Default: `noreply@mastra.ai`)

## Returns

**prompt** (`string`): The base system prompt for the coding agent.

## Related

- [`createCodingAgent()`](https://mastra.ai/reference/coding-agent/create-coding-agent)