n8n-binary-and-data

n8n Binary and Data

n8n handles two kinds of data: JSON (in $json) and binary (in $binary), flowing side-by-side. Binary has sharp edges around agent tools, storage, and display contexts (chat surfaces, message rendering).

For tabular storage (Data Tables), see the n8n-data-tables skill.

Non-negotiables

1. Binary is in $binary, not $json. Don't read file contents from $json.
2. Binary cannot cross the agent tool boundary in either direction. Tool parameters are JSON only (via fromAi()), and tool results are JSON only. Pre-stage binary in storage and pass keys/URLs through JSON. The agent's passthroughBinaryImages: true lets the LLM see uploaded images for vision, but it does NOT enable tools to receive them. See references/AGENT_TOOL_BINARY.md.

Strong defaults

• Merge nodes keep binary in context. When a side computation strips binary, merge it back rather than re-fetching. See references/MERGE_FOR_CONTEXT.md.

Binary basics

In n8n, each item has two slots:

{
    json: { ... },           // your data
    binary: {                // your files
        data: {              // 'data' is the typical key; can be any name
            data: '<base64>',
            mimeType: 'application/pdf',
            fileName: 'invoice.pdf',
            fileExtension: 'pdf',
        },
    },
}

$binary.<key> reads the named property. Most file-handling nodes have a binaryPropertyName parameter, the key inside $binary.

Setting binary

File-producing nodes (HTTP Request with binary response, Read Files, etc.) populate $binary automatically. To produce binary in a Code node:

return [{
    json: { ... },
    binary: {
        data: {
            data: Buffer.from(content).toString('base64'),
            mimeType: 'text/plain',
            fileName: 'output.txt',
        },
    },
}]

Reading binary

// In a Code node
const buffer = await this.helpers.getBinaryDataBuffer(0, 'data')
const text = buffer.toString('utf-8')

Most workflows don't need to read binary directly. Pass it through to consumer nodes (email attachments, file uploads, etc.).

See references/BINARY_BASICS.md for more.

Agent tool gymnastics

Agent tools (sub-workflows wired into a LangChain Agent, or workflows exposed as MCP tools) have a constraint: parameters and results are JSON, not binary. Affects both directions.

Inbound (user uploads → tool consumes): the chat trigger gives files[]. The agent can have passthroughBinaryImages: true for vision, but fromAi() can't pass binary to a tool. So:

1. Pre-stage uploaded files: hash a key, upload to private storage.
2. Inject the keys into the agent's system prompt: "Files passed in: [{originalFileName, fileName}]. Use EXACTLY the fileName field when calling tools."
3. The tool's fromAi('imageName', '...', 'string') receives the key. The sub-workflow downloads from storage.

Outbound (tool produces → agent returns): a tool generates a file. It can't return raw binary.

1. Generate binary internally.
2. Upload to storage, get back URL/key.
3. Return JSON: { ok: true, file_id: '...', url: '...' }.
4. The agent embeds the URL in its response, or another tool fetches by key.

For the full pattern including the async-via-webhook variant for long-running tools, see references/AGENT_TOOL_BINARY.md.

Merge for keeping binary in context

A JSON-only operation (Edit Fields, Code, IF) often strips binary from the item. To keep it:

[Source with binary] ─┬─→ [Edit Fields: transform JSON] ─┐
                      │                                    ├─→ [Merge: by position] ─→ [Email with attachment]
                      └─────────────────────────────────────┘

Merge combines the streams, and binary survives. See references/MERGE_FOR_CONTEXT.md.

CDN requirement for chat surfaces

When a workflow generates an image and the user wants it embedded in a chat message (Slack, Discord, Teams, Telegram, embedded webhook chat, etc.):

• Binary on the item isn't enough. Chat surfaces don't read $binary; they render messages that reference images by URL (or via platform-specific file upload APIs).
• The image must live somewhere a URL can fetch. Upload to a CDN or object store first.
• The user configures this storage. Not built into n8n.

Common options span object storage (S3, R2, GCS, Azure Blob, Vercel Blob, Supabase Storage) and drive-style services (Dropbox, Google Drive, OneDrive, Box). Ask the user what they use rather than defaulting to S3.

See references/CDN_REQUIREMENT.md.

Data Tables

For Data Tables, see the n8n-data-tables skill. Distinct surface with its own gotchas (default columns, no foreign keys, no JSON column type, manual-mapping UI quirk).

Reference files

File	Read when
references/BINARY_BASICS.md	First time handling binary, or reading/writing the $binary slot
references/AGENT_TOOL_BINARY.md	Agent tool needs a user-uploaded file, or produces a file (the boundary in either direction)
references/MERGE_FOR_CONTEXT.md	Binary disappears after a JSON transform and needs to re-attach
references/CDN_REQUIREMENT.md	Showing images in a chat surface or other places that need URL-referenced images

Anti-patterns

Anti-pattern	What goes wrong	Fix
Trying to read file content from $json	Binary isn't in $json	Use $binary
Building an agent tool that returns binary directly	Tool output is JSON-only, so binary doesn't survive	Upload to storage, return key/URL in JSON (see AGENT_TOOL_BINARY.md)
Trying to pass uploaded chat files into a tool via fromAi	fromAi doesn't carry binary, so the tool gets nothing	Pre-stage uploads to storage, inject keys in the system prompt, and have the tool download by key
Setting passthroughBinaryImages: true and assuming tools can now see the file	The flag only affects what the LLM sees, not what tools receive	Still need the upload-and-pass-key pattern for tools
Losing binary after a JSON transform	The transform's output item doesn't have binary	Use Merge to combine the JSON output with the binary stream
Storing image in n8n binary and expecting a chat surface to display	Chat surfaces need URL-accessible images (or a platform-native file upload), not raw $binary	Upload to CDN, embed URL or use the platform's file API
Hardcoding binary base64 in a Code node	Massive workflow JSON, slow, leaky	Reference binary via $binary properly, or upload to storage and reference by URL