n8n-nodes-anthropic-structured

An n8n community chat-model node that wraps Anthropic Claude and exposes Anthropic's constrained-decoding structured-output API (output_config.format) as a first-class option. Set a JSON Schema, and the model is guaranteed to return schema-conformant JSON — no prompt-injected formatting instructions, no optional tool the model can ignore.

A drop-in alternative to n8n's built-in Anthropic Chat Model for any workflow that needs reliable structured output.

Why this exists

n8n's stock Anthropic node uses LangChain, which (as of early 2026) implements structured output via the legacy tool-use trick — define a synthetic format_final_json_response tool and hope the model calls it. This is unreliable on medium-complex schemas: the model can produce free-form text, or call the tool with malformed args, or ignore it entirely.

Anthropic shipped real constrained decoding — output_config.format with type: "json_schema". The schema is enforced at the sampling layer: every emitted token has to match. LangChain hasn't picked this up yet. This node does.

Installation

In your n8n instance:

1. Go to Settings → Community Nodes
2. Click Install a community node
3. Enter n8n-nodes-anthropic-structured and accept the risk acknowledgement

Setup

1. Create or open a workflow.
2. Add an AI Agent, Basic LLM Chain, or any node with an ai_languageModel input.
3. On the Chat Model input click +, search Anthropic (Structured).
4. Configure an Anthropic API credential (x-api-key header — get a key at console.anthropic.com).
5. Pick a Claude model (4.5+ — only those support output_config.format).
6. (Optional) Paste a JSON Schema into the JSON Schema field. When non-empty, every response is constrained-decoded against that schema.

With and without tools

• Without tools (Basic LLM Chain): the single response is JSON-schema conformant. Standard use case.
• With tools (AI Agent + tool nodes): intermediate agent rounds emit tool_use blocks as normal; the model's final answer is the schema-conformant JSON. Anthropic explicitly supports this composition.

Supported Claude models

• Claude Opus 4.7 / 4.6 / 4.5
• Claude Sonnet 4.6 / 4.5
• Claude Haiku 4.5

Earlier Claude models don't support output_config.format and aren't listed in the model picker.

How it works

Verified-community-node compliant — uses only @n8n/ai-node-sdk and standard fetch, no third-party SDKs in the published bundle:

• Extends BaseChatModel from @n8n/ai-node-sdk
• Implements generate() / stream() by POSTing to https://api.anthropic.com/v1/messages directly
• Maps n8n's Message/MessageContent types to Anthropic's request shape (system messages extracted to the top-level system field, tool-call/tool-result content blocks translated to Anthropic's tool_use/tool_result)
• Tools bound by the agent via withTools() are sent as Anthropic tool definitions; input_schema type is backfilled to "object" when missing so Anthropic accepts schemas like {} from tools without parameters
• When jsonSchema is set, includes output_config: { format: { type: "json_schema", schema } }

See nodes/AnthropicStructured/helpers.ts for the conversion functions (covered by vitest tests).

Credentials

The Anthropic API credential takes a single field:

• API Key — your Anthropic API key (sent as the x-api-key header along with anthropic-version: 2023-06-01)

The credential test issues a GET /v1/models against the Anthropic API.

Compatibility

• n8n >= 2.19
• Self-hosted and (once verified) n8n Cloud
• Zero third-party runtime dependencies

Development

pnpm install      # install deps
pnpm lint         # n8n's community-node lint suite
pnpm test         # vitest unit tests
pnpm build        # compile TypeScript and copy static files into dist/
pnpm dev          # run a local n8n with this node loaded (hot reload)

CI runs lint + tests + build on every push and PR. Releases are triggered by pushing a version tag (e.g. 0.1.1); GitHub Actions then publishes to npm with a provenance attestation.

Resources

• Anthropic structured outputs docs
• Anthropic Messages API reference
• n8n community node docs

License

MIT