n8n-binary-and-data

1# n8n Binary and Data
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3Every n8n item carries two independent slots: `$json` for structured data and `$binary` for file bytes. They travel side by side through the workflow. File contents — the actual PDF, image, or zip — live in `$binary`, never in `$json`. Get that split wrong and you read an empty field, lose a file mid-flow, or hand an AI agent a tool input it can't use.
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5This skill covers where binary lives, how to read and write it, how to keep it from being silently stripped, the hard wall between binary and the AI-agent tool boundary, and why chat surfaces need a URL instead of raw bytes.
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9## The three rules that prevent 90% of binary bugs
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111. **File contents are in `$binary`, not `$json`.** After an HTTP download, a "Read Files", or an email-attachment trigger, the bytes sit in `$binary.<key>`. `$json` holds metadata at most. Reading `$json.data` for file contents gives you nothing.
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132. **Binary cannot cross the AI-agent tool boundary — in either direction.** Tool arguments and tool return values are JSON only. An uploaded image can't be passed into a tool as a file, and a tool can't return raw bytes. Pre-stage to storage and pass a key or URL through JSON instead. See `AGENT_TOOL_BINARY.md`.
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153. **Chat surfaces render images by URL, not by `$binary`.** Slack, Discord, Teams, Telegram, embedded webhook chat — none of them read the binary slot. The image has to live somewhere a URL can fetch it. See `CDN_REQUIREMENT.md`.
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19## The two slots
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