Adapter

Adapter modules connect external models, tools, and protocol ecosystems to Rejelly. Adapters fall into two categories by responsibility:

• Model Adapters: Wrap provider models into Rejelly's ModelAdapter, see Model Adapter (OpenAI / Gemini).
• Tool / Source Adapters: Convert external tool ecosystems into Rejelly ToolDefinition, see MCP and LangChain.

Adapters have been extracted from @rejelly/core and published as separate packages. Install the corresponding package as needed:

Package	Purpose
@rejelly/adapter-openai	OpenAI model adapter, provides createOpenAIAdapter
@rejelly/adapter-gemini	Gemini model adapter, provides createGeminiAdapter
@rejelly/adapter-mcp	MCP tool / resource / prompt integration, provides equipMCP / fromMCPTool
@rejelly/adapter-langchain	LangChain tool adapter, provides fromLangChainTool

Multimodal Tool Results

Tools can return model-visible multimodal content (e.g., images) by wrapping the result with toolContent(parts: ContentPart[]) from @rejelly/core. Regular JSON / string results are still stringified as-is; only objects marked by toolContent enter the conversation as MessageContent. The two adapter categories each handle this on their respective side:

Model adapter (OpenAI / Gemini) — send-side auto-splitting. Most providers only allow text in tool / function result messages. When a tool message contains media (e.g., an image returned via toolContent), the message converter automatically splits it into two messages: a plain-text tool result + an immediately following user message carrying the media, so the model can actually "see" the image. Plain-text tool results are unaffected and remain as a single message.

• OpenAI (toOpenAIMessages): tool (text, placeholder sentence when purely media) → user (image_url).
• Gemini (toGeminiMessages): functionResponse (text) → user Content (inlineData). Note this produces two consecutive client-side turns (function directly followed by user).

This is normalization performed by the adapter at the "provider capability boundary": only the adapter layer knows which providers cannot carry images in tool results. Hence this conversion lives in the adapter, transparent to all policies and upper-level Agents — no metatool or extra round-trips needed.

Tool / source adapter (MCP / LangChain) — receive-side conversion to toolContent. When a tool itself returns multimodal content blocks (including images), the adapter converts them into toolContent so they flow as native model-visible content into the send-side above; plain text or unrecognized results pass through unchanged, preserving existing behavior.

• MCP (formatCallToolResult): image blocks → image ContentPart; resource blocks degraded by text/label.
• LangChain (fromLangChainTool): Classic image_url and standard image (source_type: "base64" | "url") blocks in content-block arrays → image ContentPart.