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generate_messages_api_v1_messages_post

Converts Anthropic Messages API requests to OpenAI Chat Completions format, processes through Open WebUI, and returns responses in Anthropic format for any configured model.

Instructions

Anthropic Messages API compatible endpoint.

Accepts the Anthropic Messages API format, converts internally to OpenAI Chat Completions format, routes through the existing chat completion pipeline, then converts the response back to Anthropic Messages format.

Supports both streaming and non-streaming requests. All models configured in Open WebUI are accessible via this endpoint.

Authentication: Supports both standard Authorization header and Anthropic's x-api-key header (via middleware translation).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
form_dataYes
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It mentions streaming support and authentication headers, but does not disclose error handling, rate limits, state changes, or response structure beyond conversion.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise, front-loaded with the key purpose, and covers conversion, streaming, model availability, and authentication in a few sentences without wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the absence of output schema and annotations, the description should explain expected response format (Anthropic Messages API) and provide more behavioral details. It mentions response conversion but lacks specifics on error handling, streaming behavior, and limits.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter `form_data` is an object with additionalProperties true and 0% schema description coverage. The description implies it should contain the Anthropic Messages API request body, but does not explicitly describe the required fields or format, nor does it compensate sufficiently.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states it is an Anthropic Messages API compatible endpoint that converts to OpenAI Chat Completions, distinguishing it from sibling tools like chat_completion_api_v1_chat_completions_post which likely accepts OpenAI format directly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explains that the endpoint converts Anthropic format to OpenAI internally, implying it is for clients using Anthropic API format, but does not explicitly state when to use this vs direct chat_completion, nor does it mention any alternatives or exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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