fix: replace z.base64() with z.string() for Gemini compatibility#10
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RaviTharuma wants to merge 1 commit intoagentmail-to:mainfrom
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fix: replace z.base64() with z.string() for Gemini compatibility#10RaviTharuma wants to merge 1 commit intoagentmail-to:mainfrom
RaviTharuma wants to merge 1 commit intoagentmail-to:mainfrom
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z.base64() generates `contentEncoding: "base64"` in the JSON Schema output (via zod-to-json-schema). Google Gemini's function calling API does not support `contentEncoding` in its schema subset, causing 400 errors when registering tools that use this field. Replacing with z.string() preserves the same runtime behavior (base64 strings are valid strings) while producing a Gemini-compatible schema. The description already indicates the expected format is base64. Fixes agentmail-to/agentmail-mcp#8
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Summary
z.base64()withz.string()inAttachmentSchema.contentfieldz.base64()generatescontentEncoding: "base64"in JSON Schema output, which Google Gemini's function calling API does not supportsend_message,reply_to_message,forward_message)Problem
When MCP tools are registered with Gemini models, the generated JSON Schema includes:
{ "content": { "type": "string", "contentEncoding": "base64", "format": "base64", "pattern": "^$|^(?:[0-9a-zA-Z+/]{4})*..." } }Gemini only supports a subset of JSON Schema (
type,description,enum,items,properties,required,format,nullable) and rejectscontentEncodingwith:Fix
z.string()produces a clean{"type": "string"}schema that all providers accept. The.describe('Base64 encoded content')already communicates the expected format to the LLM. Runtime behavior is unchanged since base64 strings are valid strings.References
Summary by cubic
Replace AttachmentSchema.content from z.base64() to z.string() to produce Gemini-compatible JSON Schema. This removes the unsupported contentEncoding field and fixes 400 errors when registering tools with attachments (e.g., send_message, reply_to_message, forward_message).
Written for commit 8dbea9e. Summary will update on new commits.