Use Mastra

Prerequisites

Before writing Mastra code, verify the relevant package is installed in the current project:

ls node_modules/mastra 2>/dev/null          # CLI + project scaffolding + platform API
ls node_modules/@mastra/ 2>/dev/null        # scoped packages (core, memory, rag, ...)

If the needed package is missing, install only what the task requires using the project's package manager (detect via lockfile):

# root CLI / platform (only when invoking `mastra dev`, `mastra build`, etc.)
pnpm add mastra        # or: bun add mastra / npm i mastra / yarn add mastra

# scoped packages — add what you actually use
pnpm add @mastra/core @mastra/memory @mastra/rag

Do not install packages you do not yet need. Mastra is opinionated about module format — confirm TypeScript target before writing: target: ES2022, module: ES2022, moduleResolution: bundler.

Critical: Do Not Trust Internal Knowledge

Mastra evolves rapidly. Constructor signatures, exported symbol names, workflow step APIs, memory option shapes, and model-router providers shift between minor versions. Training-data recollection of Mastra APIs is likely wrong.

When working with Mastra:

1. Resolve the installed version first (node_modules/<pkg>/package.json).
2. Read the SKILL.md shipped inside that version at node_modules/<pkg>/dist/docs/SKILL.md before coding.
3. Verify every constructor, export, and option against dist/docs/references/*.md or dist/docs/assets/SOURCE_MAP.json.
4. Run typecheck after every change — Mastra APIs are type-heavy and silent drift is rare.
5. Never invent provider strings, plugin names, or adapter imports. Enumerate first.
6. Surface deprecations to the user instead of silently picking one pattern.

If documentation cannot be found locally or remotely to back an answer, say so explicitly.

Finding Documentation

Bundled docs in node_modules/

Every Mastra package that ships documentation places it at <pkg>/dist/docs/:

node_modules/<pkg>/dist/docs/
├── SKILL.md                       # package overview + links
├── assets/SOURCE_MAP.json         # export → source file mapping
└── references/                    # one .md per topic or exported symbol
    ├── docs-<topic>.md            # concept guides
    └── reference-<symbol>.md      # API reference

Packages confirmed to ship dist/docs/ (v1.6.2 / core 1.27.0 as of 2026-04):

See references/packages.md for purpose + SKILL path per package, plus which packages currently lack bundled docs (remote-only).

Canonical lookup flow

# 1. Start from the overview shipped with the installed version
cat node_modules/@mastra/core/dist/docs/SKILL.md

# 2. Grep references/ for the topic or symbol
grep -rli "Agent" node_modules/@mastra/core/dist/docs/references/
grep -rli "createWorkflow" node_modules/@mastra/core/dist/docs/references/

# 3. Resolve an exported symbol back to its type definition
cat node_modules/@mastra/core/dist/docs/assets/SOURCE_MAP.json | jq '."Agent"'
cat node_modules/@mastra/core/dist/<path-from-source-map>

Remote fallbacks

If the package is not installed, or a doc is missing from dist/docs/:

1. https://mastra.ai/llms.txt — index of current docs (fetch and grep).
2. https://mastra.ai/docs/ — full documentation site.
3. The @mastra/mcp-docs-server MCP server (configured by this plugin in plugin.json) — returns the same docs over MCP tool calls.

Remote docs track main and may be ahead of the installed version; always prefer bundled docs when both are available.

Mastra Package Map

Concise map of what each package exports and where its docs live. Full table with docs paths and verification notes: references/packages.md.

Building Agents & Workflows

Concise recipes — each one ends with "verify against dist/docs/ before shipping": references/agents-and-workflows.md.

Rules of thumb:

• Agent vs Workflow. Use Agent for open-ended tasks (research, chat, triage). Use createWorkflow + createStep for deterministic pipelines with a fixed shape and explicit state.
• Register everything on Mastra. Tools, agents, workflows, storage, and logger all hang off a single Mastra instance. Passing tools to an agent without also registering them on Mastra is a common bug.
• Model strings. Always provider/model (e.g. openai/gpt-5.4, anthropic/claude-sonnet-4-5). Never bare model IDs. The provider-registry script shipped with the existing mastra skill (plugins/mastra/.agents/skills/mastra/scripts/provider-registry.mjs) enumerates valid provider keys and current model names — run it before generating code that references a model.
• .commit() is required on workflows. Forgetting it is the #1 cause of Cannot read property 'then' of undefined.
• threadId + resourceId must be stable across turns for memory to persist.
• Typecheck after every change: pnpm tsc --noEmit (or bun tsc --noEmit, npm run typecheck).

When Typecheck or Runtime Fails

Before searching source code, grep references/common-errors.md for the failing symptom. It indexes the most frequent Mastra failure modes (ESM/CJS mismatch, tools registered but not called, memory without storage, semantic recall without a vector store, workflow missing .commit(), invalid model string, wrong threadId) against the canonical fix.

If the symptom is not listed:

# resolve the error string inside installed source
rg -n "error string fragment" node_modules/@mastra/core/dist
rg -n "error string fragment" node_modules/@mastra/<subpkg>/dist

Relationship to the mastra skill

This plugin ships a separate, richer primer at plugins/mastra/.agents/skills/mastra/SKILL.md (v2.0.0, sourced from mastra-ai/skills). That skill is a framework primer — concepts, doc-lookup strategy, upgrade guides, migration notes, extensive common-errors coverage.

use-mastra is the task-triggered workflow skill — concise, trigger-heavy, focused on redirecting agents to version-accurate dist/docs/ and stopping training-data hallucinations. The two are complementary; Claude Code will auto-activate whichever matches the task framing.

When in doubt, read the primer first (plugins/mastra/.agents/skills/mastra/SKILL.md) and use this skill's references for quick per-package lookup paths and concise recipes.

References

• references/packages.md — every Mastra package, its purpose, and the exact dist/docs/ path to read
• references/agents-and-workflows.md — canonical recipes: agent with tools + memory, workflow with steps, Mastra-instance registration
• references/common-errors.md — symptom → cause → fix for the most frequent Mastra failures