diff --git a/packages/builtin-tools/src/tools/ArtifactTool/prompt.ts b/packages/builtin-tools/src/tools/ArtifactTool/prompt.ts
new file mode 100644
index 000000000..ab0ebe5f1
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+++ b/packages/builtin-tools/src/tools/ArtifactTool/prompt.ts
@@ -0,0 +1,25 @@
+export const ARTIFACT_TOOL_NAME = 'artifact'
+
+export async function describeArtifactTool(): Promise<string> {
+  return 'Upload an HTML file to the cloud-artifacts hosting service and get back a public URL. Pass `hash` to overwrite a previously-uploaded artifact (keeps URL stable).'
+}
+
+export async function getArtifactToolPrompt(): Promise<string> {
+  return `Upload an HTML file to a public hosting service and return a shareable URL plus an internal \`id\` (the "hash").
+
+## Inputs
+- \`file_path\` (required): absolute path to a local HTML file.
+- \`hash\` (optional): if provided, overwrites the artifact with the same hash (URL stays the same). If omitted, a new random id is generated.
+- \`ttl\` (optional, default \`7\`): artifact lifetime in days. Must be \`7\` or \`30\`.
+
+## Output
+\`{ id, url, expiresAt }\` — \`id\` is the hash (save it for future overwrite calls), \`url\` is publicly accessible.
+
+## Workflow
+1. Use the Write tool to create a local HTML file.
+2. Call this tool with its \`file_path\`.
+3. If iterating on the same artifact, pass back the \`id\` returned from the first call as \`hash\` so the URL stays stable.
+
+## Errors
+The tool surfaces backend error codes verbatim (e.g. \`payload_too_large\`, \`unauthorized\`). If the file does not exist or is not a regular file, the tool returns an \`error\` field without making an HTTP request.`
+}