Configuration

Mastra Code is configured through project-level files, global settings, and environment variables. Configuration files live in .mastracode/ directories at the project and user levels.

Authentication

Mastra Code supports two authentication methods: API keys (environment variables) and OAuth (provider subscriptions). You can use either or both.

API keys

The simplest way to get started is to set API key environment variables for the providers you want to use. Mastra Code auto-detects these on startup:

export ANTHROPIC_API_KEY=sk-ant-...
export OPENAI_API_KEY=sk-...
export GOOGLE_GENERATIVE_AI_API_KEY=...
export DEEPSEEK_API_KEY=...
export CEREBRAS_API_KEY=...

Mastra Code uses Mastra's model router, which routes requests to the correct provider based on the model ID and available API keys. No OAuth login is required when using API keys.

If you have an Anthropic Claude Max or OpenAI ChatGPT Plus subscription, you can authenticate via OAuth to use your subscription instead of API keys. Run /login in the TUI to start the flow.

Provider	OAuth flow	What you get
Anthropic	Claude Max subscription	Access to Claude models via your subscription
OpenAI	ChatGPT Plus / Codex	Access to OpenAI models via your subscription

OAuth credentials are stored in auth.json alongside the database in the app data directory. During onboarding, you can skip the OAuth step if you already have API keys configured.

Anthropic OAuth warning

Authenticating with a Claude Max subscription through OAuth is a grey area. Anthropic has reportedly banned users for using Claude max credentials outside of Claude Code, so it may violate Anthropic Terms of Service.

MCP servers

Mastra Code can connect to external MCP servers and make their tools available to the agent. Configure servers in JSON files:

Priority	Path	Scope
Highest	`.mastracode/mcp.json`	Project
	`~/.mastracode/mcp.json`	Global
Lowest	`.claude/settings.local.json`	Project (Claude Code compatible)

Project config overrides global config by server name. Claude Code settings are the lowest priority fallback.

MCP config format

.mastracode/mcp.json
{
  "mcpServers": {
    "my-server": {
      "command": "npx",
      "args": ["-y", "@my-org/mcp-server"],
      "env": {
        "API_KEY": "your-key"
      }
    }
  }
}

Each server entry requires a command field. The args and env fields are optional.

On startup, Mastra Code connects to all configured servers and reports the status:

MCP: 2 server(s) connected, 15 tool(s)

Tools from MCP servers are namespaced as serverName_toolName and appear in the agent's tool list alongside built-in tools.

Hooks

Hooks are user-configured shell commands that run at specific lifecycle events. Use hooks for custom validation, logging, notifications, or integration with external systems.

Hook config format

.mastracode/hooks.json
{
  "PreToolUse": [
    {
      "type": "command",
      "command": "node scripts/validate-tool.js",
      "matcher": {
        "tool_name": "execute_command"
      },
      "timeout": 5000,
      "description": "Validate shell commands before execution"
    }
  ],
  "PostToolUse": [
    {
      "type": "command",
      "command": "node scripts/log-tool.js",
      "description": "Log tool usage"
    }
  ]
}

Hook events

Event	When it fires	Can block?
`PreToolUse`	Before a tool call executes	Yes
`PostToolUse`	After a tool call completes	No
`Stop`	When an agent response ends (`complete`, `aborted`, or `error`)	Yes
`UserPromptSubmit`	When the user sends a message	Yes
`SessionStart`	When a session begins	No
`SessionEnd`	When a session ends	No
`Notification`	When the TUI fires a notification	No

UserPromptSubmit runs before a non-command prompt is sent to the agent. If a hook blocks, the prompt is not sent.

Hook I/O protocol

Hook processes receive a JSON payload on stdin with context about the event:

{
  "session_id": "thread-abc123",
  "cwd": "/path/to/project",
  "hook_event_name": "PreToolUse",
  "tool_name": "execute_command",
  "tool_input": { "command": "npm test" }
}

For blocking events (PreToolUse, Stop, UserPromptSubmit), the hook can respond on stdout with a JSON object:

{
  "decision": "block",
  "reason": "This command is not allowed"
}

Hook config locations

Priority	Path	Scope
Higher	`.mastracode/hooks.json`	Project (appended after global)
Lower	`~/.mastracode/hooks.json`	Global (runs first)

Global hooks run before project hooks. For the same event, all hooks execute in order.

Custom slash commands

Define reusable prompt templates as markdown files. Mastra Code scans these directories for .md files:

Priority	Path	Scope
Highest	`.mastracode/commands/`	Project
	`.claude/commands/`	Project (Claude Code compatible)
	`~/.mastracode/commands/`	Global
Lowest	`~/.claude/commands/`	Global (Claude Code compatible)

Each command file can include YAML frontmatter with name and description fields:

.mastracode/commands/review.md
---
name: review
description: Review the current diff for issues
---
Review my current git diff. Look for bugs, security issues,
and violations of the project's coding standards.

The filename (or directory structure) determines the command name. For example, git/commit.md becomes /git:commit.

Commands support variables like $ARGUMENTS for positional args, @filename for file content injection, and !command for shell command output.

Skills

Skills are structured instruction files that the agent loads automatically based on trigger conditions. They provide domain-specific guidance without manually pasting instructions.

Mastra Code scans these directories for skills:

Priority	Path	Scope
Highest	`.mastracode/skills/`	Project
	`.claude/skills/`	Project (Claude Code compatible)
	`~/.mastracode/skills/`	Global
Lowest	`~/.claude/skills/`	Global (Claude Code compatible)

Each skill is a directory containing a SKILL.md file with instructions and trigger descriptions. Skills installed via symlinks (e.g., from npx skills add) are automatically resolved.

Agent instructions

Mastra Code loads project-specific instructions from AGENTS.md or CLAUDE.md files and injects them into the agent's system prompt. This is how you can customize the agent's behavior for your project.

Lookup order

For project instructions (first match wins):

AGENTS.md or CLAUDE.md in the project root
.claude/AGENTS.md or .claude/CLAUDE.md
.mastracode/AGENTS.md or .mastracode/CLAUDE.md

For global instructions (first match wins):

~/.claude/AGENTS.md or ~/.claude/CLAUDE.md
~/.mastracode/AGENTS.md or ~/.mastracode/CLAUDE.md
~/.config/claude/AGENTS.md or ~/.config/claude/CLAUDE.md
~/.config/mastracode/AGENTS.md or ~/.config/mastracode/CLAUDE.md

AGENTS.md takes priority over CLAUDE.md when both exist at the same location.

Storage

Mastra Code stores threads, messages, state, and observational memory in a database. It uses LibSQL by default with a local file — no setup needed.

To switch to a remote LibSQL (Turso) or PostgreSQL backend, run /settings and select a storage backend. You'll be prompted for a connection URL.

If a PostgreSQL connection fails on startup, Mastra Code falls back to LibSQL and shows a warning so you can fix the connection via /settings.

Observational memory

Observational memory (OM) uses background agents to maintain a dense log of observations and reflections about the conversation, providing long-term context that persists across sessions.

OM scope

Control whether observations are scoped to individual threads or shared across all threads for a project:

Scope	Behavior
`thread` (default)	Observations are private to each conversation thread
`resource`	Observations are shared across all threads for the same project

Configure the scope through:

MASTRA_OM_SCOPE environment variable ("thread" or "resource")
.mastracode/database.json → omScope field
~/.mastracode/database.json → omScope field

OM model settings

The observer and reflector models default to google/gemini-2.5-flash. Override them per-thread through the /settings panel or in the harness state.

OM thresholds

Threshold	Default	Description
Observation threshold	30,000 tokens	Token count that triggers an observation pass
Reflection threshold	40,000 tokens	Token count that triggers a reflection pass

Color theme

Mastra Code detects your terminal's color scheme and applies a matching dark or light theme. You can override the detected theme with the /theme slash command or the MASTRA_THEME environment variable.

Detection order

MASTRA_THEME environment variable — explicit dark or light
Persisted setting from /theme command (stored in settings.json)
OSC 11 query — asks your terminal for its actual background color
COLORFGBG environment variable (set by some terminals like iTerm2 and Konsole)
Falls back to dark theme

Switching themes

Use the /theme command to change the theme at runtime:

/theme light
/theme dark
/theme auto

Running /theme with no arguments shows the current theme. The choice is persisted across sessions.

Environment variables

Variable	Description
`MASTRA_DB_URL`	LibSQL database URL (e.g., `libsql://...` or `file:./data.db`)
`MASTRA_DB_AUTH_TOKEN`	Auth token for remote LibSQL database
`MASTRA_DB_PATH`	Override the local database file path
`MASTRA_USER_ID`	Override the auto-detected user identity
`MASTRA_RESOURCE_ID`	Override the auto-detected project resource ID
`MASTRA_OM_SCOPE`	Observational memory scope (`thread` or `resource`)
`DEFAULT_OM_MODEL_ID`	Default model for OM observer and reflector
`MASTRA_THEME`	Color theme override (`dark` or `light`)
`TAVILY_API_KEY`	Enable Tavily-powered web search and extract tools

Resource ID override

Resource IDs determine how threads are grouped. By default, Mastra Code generates one from the Git remote URL or filesystem path. Override it to share threads across repositories or isolate threads within a monorepo:

.mastracode/database.json
{
  "resourceId": "my-custom-project-id"
}

You can also set MASTRA_RESOURCE_ID as an environment variable. Two users who set the same resource ID share threads and observations for that resource.

Authentication​

API keys​

OAuth login (optional)​

Anthropic OAuth warning​

MCP servers​

MCP config format​

Hooks​

Hook config format​

Hook events​

Hook I/O protocol​

Hook config locations​

Custom slash commands​

Skills​

Agent instructions​

Lookup order​

Storage​

Observational memory​

OM scope​

OM model settings​

OM thresholds​

Color theme​

Detection order​

Switching themes​

Environment variables​

Resource ID override​