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() when you build dynamic instructions for the agent.

Usage example

Build the base prompt from a PromptContext:

src/mastra/prompt.ts

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:

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

= Mastra Code

Display name used in the prompt header.

coAuthorName?:

string

= Mastra Code

Name used in the commit Co-Authored-By line.

coAuthorEmail?:

string

= noreply@mastra.ai

Email used in the commit Co-Authored-By line.

Returns

prompt:

string

The base system prompt for the coding agent.

Related

• createCodingAgent()