Handle files and binary data in n8n correctly. Use when working with files, images, PDFs, attachments, uploads or downloads, base64, vision/multimodal input, or when an AI agent needs a file as tool input or output — and whenever the user mentions $binary, binaryPropertyName, "read the PDF", "attach

n8n Binary and Data Every 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. This 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. The three rules that prevent 90% of binary bugs 1. 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. 2. 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 . 3. 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 . The two slots Each item is shaped like this: The key inside binary ( invoice here) is the binary property name . Most file handling nodes have a binaryPropertyName parameter that points at it — the producer names the slot, the consumer references it by that name. The default key across most nodes is data , so when nothing tells you otherwise, assume $binary.data . $json and $binary are separate namespaces. An expression like {{ $binary.invoice.fileName }} reads file metadata; {{ $json.customerId }} reads data. They never mix. This split also explains a webhook gotcha: a Webhook trigger receiving multipart/form data puts the uploaded file in $binary and the accompanying form fields in $json.body — so an uploaded file is not somewhere under $json at all. (The $json.body nesting for webhooks is n8n expression syntax territory.) See BINARY BASICS.md for the full slot anatomy, mime types, and size limits. Producing binary You rarely build a $binary slot by hand — nodes populate it for you: Source How binary appears HTTP Request with responseFormat: "file" Response body lands in $binary.data (or the name you set) Read/Write Files from Disk File contents read into $binary Storage downloads (S3, Google Drive, Dropbox, etc.) Downloaded file in $binary.<key Email triggers with attachments Each attachment arrives in $binary Provider AI media nodes (image/audio gen) Set options.binaryPropertyOutput so the bytes land where the next node looks For an HTTP download, the one field that matters is responseFormat . Confirm it with get node on nodes base.httpRequest — leaving it as the default JSON/string format is the classic reason a downloaded file ends up as garbled text in $json instead of clean bytes in $binary . Reading and writing binary in a Code node Most workflows never need to crack open the bytes — they just pass binary through to a consumer (email attachment, file upload, Slack file). When you do need the raw bytes, do it in a Code node. Read with getBinaryDataBuffer — do not try to base64 decode $binary.<key .data by hand: Write by building the slot yourself — base64 the bytes plus a mime type and file name: The Code node sandbox, helpers, and execution modes are the domain of n8n code javascript (and n8n code python ) — use those for the language level detail. The one binary specific thing to remember here: a Code node that returns [{ json: {...} }] without re attaching binary silently drops the file . See BINARY BASICS.md . Keeping binary alive across transforms JSON only nodes — Edit Fields (Set), Code, IF, and others — can drop the $binary slot from their output. The workflow validates clean and runs without error; the file just isn't there downstream when the email node goes to attach it. Two ways to keep it: Pass through option on the transforming node. Edit Fields has includeOtherFields ; a Code node can return binary: $input.item.binary explicitly. Cheapest fix when it's available. Fan out and Merge by position. Route the source into both the transform and a bypass branch, then recombine with a Merge in combineByPosition mode. The JSON comes from the transform side, the binary survives on the bypass side. combineByPosition pairs item N from each input, so the field counts must line up. The connection wiring and the alternatives for many strip point chains (upload early, sub workflow) are in MERGE FOR CONTEXT.md . The agent tool binary boundary This is the sharpest edge. An AI Agent talks to its tools (Custom Code Tool, Call n8n Workflow Tool, HTTP Request Tool, MCP tools) over JSON. Binary does not fit through that pipe in either direction. The fix is the same shape both ways: stage the bytes in storage, pass a key/URL through JSON, fetch on the other side. Inbound — a user uploads a file the agent's tool must operate on: 1. The chat trigger gives you a files[] array. Split it out and upload each file to private storage under a hashed key. 2. Re merge that branch before the agent runs (it's a synchronization barrier, not decoration), and set executeOnce: true on the agent so N files don't trigger N agent runs. 3. Inject the keys into the agent's system prompt, listing both the original name (human context) and the storage key (what the tool needs), with an explicit "use EXACTLY this key". 4. The tool receives the key as a string argument and downloads the file from storage itself. Outbound — a tool generates a file the agent must return: 1. The tool sub workflow generates the binary, uploads it to storage, and returns JSON like { "ok": true, "key": "...", "url": "https://...", "mimeType": "image/png" } . 2. The agent embeds the URL in its reply (or passes the key to another tool). passthroughBinaryImages: true on the agent only changes what the LLM sees for vision — it does not let tools receive the file, and it's image only (no PDFs, audio, or video). You still need the upload and pass key pattern for any tool. Full patterns, hash strategy, storage choices, and the long running tool variant are in AGENT TOOL BINARY.md . Building the tool itself? See n8n code tool for the Custom Code Tool contract and n8n workflow patterns for the AI Agent with tools shape. The CDN requirement for chat surfaces When a workflow generates an image and the user wants it shown inside a chat message: Binary on the item isn't enough. The chat client renders messages that reference images by URL (or pushes bytes through the platform's own file upload API). It never reads $binary . The bytes have to live somewhere a URL can fetch over HTTPS. Upload to an object store or drive first, then embed the returned URL. n8n has no built in CDN. The user provides the storage. Ask which storage they already use rather than defaulting to S3 — object storage (S3, R2, GCS, Azure Blob, Backblaze B2, Supabase Storage) and drive style services (Dropbox, Google Drive, OneDrive, Box) all work and all change the URL shape. Cloudflare R2 is the lowest friction starting point if they have nothing. For sensitive content, use a signed URL with an expiry rather than a permanently public one. See CDN REQUIREMENT.md . What's NOT available $fromAI() cannot carry binary. It fills tool parameters with strings, numbers, booleans, and objects — never file bytes. Pass a storage key instead. Tool arguments and returns are JSON only. There is no "binary parameter" on an agent tool, in or out. n8n ships no CDN or public file host. Serving a file over a URL is always something the user's storage does, not n8n. getBinaryDataBuffer is a Code node helper. It isn't available in the Custom Code Tool sandbox (see n8n code tool ). Where Data Tables live For persistent tabular storage — reference counting staged files, tracking which keys are live, dedup — that's the n8n manage datatable surface, owned by n8n mcp tools expert . This skill does not cover Data Tables. Anti patterns Anti pattern What goes wrong Fix Reading file contents from $json Bytes live in $binary ; $json is empty or metadata only Read $binary.<key , or getBinaryDataBuffer in a Code node HTTP download without responseFormat: "file" Bytes arrive as mangled text in $json , not clean binary Set responseFormat: "file" on the HTTP Request node Code node returns [{json:{...}}] , no binary The file is silently dropped downstream Re attach binary: $input.item.binary in the return JSON transform (Edit Fields/IF) eats the binary Email/upload node finds nothing to attach Pass through option, or fan out + Merge by position Passing an uploaded file into a tool via $fromAI $fromAI can't carry binary; the tool gets nothing Pre stage to storage, inject the key in the system prompt, tool fetches by key Assuming passthroughBinaryImages lets tools see the file It only affects what the LLM sees, and only for images Still need the upload and pass key pattern for tools Tool returns raw binary to the agent Tool output is JSON; bytes don't survive (and bloat context) Upload, return { key, url } in JSON Posting $binary to a chat surface and expecting an image Chat clients render by URL, not raw bytes Upload to storage/CDN, embed the URL or use the platform file API Hardcoding base64 in a Code node Huge workflow JSON, slow, leaky Reference via $binary , or upload and reference by URL Reference files File Read when BINARY BASICS.md First time handling binary, or reading/writing the $binary slot, mime types, size limits AGENT TOOL BINARY.md An agent tool needs an uploaded file, or produces one — the boundary in either direction MERGE FOR CONTEXT.md Binary disappears after a JSON transform and you need to re attach it CDN REQUIREMENT.md Showing images in a chat surface or anywhere that needs URL referenced images Integration with Other Skills n8n code javascript / n8n code python : the Code node is where you read/write raw bytes ( getBinaryDataBuffer , Buffer.from(...).toString('base64') ). Those skills own the sandbox, helpers, and execution mode detail — this skill owns the rule that binary must be re attached on return. n8n code tool : the Custom Code Tool sandbox is narrower — no $binary , no getBinaryDataBuffer , no $fromAI . When a tool needs a file, this skill's storage key pattern is how it gets one. n8n workflow patterns : the agent tool binary boundary sits inside the AI Agent with tools pattern; the CDN flow is a generate → upload → reply chain. n8n node configuration : responseFormat , binaryPropertyName , includeOtherFields , binaryPropertyOutput are all conditional fields — use get node to confirm the exact names on the user's version. n8n expression syntax : addressing $binary.<key .fileName vs $json.body (webhook uploads in particular) is expression territory. n8n validation expert : a dropped binary slot is a silent failure — validate workflow won't flag it. Confirm presence by inspecting the execution. n8n mcp tools expert : owns n8n manage datatable (Data Tables) and n8n executions — use the latter to confirm a binary slot actually survived a given node. n8n error handling : storage uploads and downloads fail; the inbound/outbound staging steps need error branches so a missing ke

n8n-binary-and-data