fix: validate image-only attachments for OpenAI/xAI #389

mikehostetler · 2026-01-31T01:01:57Z

Problem

OpenAI and xAI only support image attachments via their Chat Completions API. Non-image files (PDFs, etc.) fail with cryptic API errors.

Add upfront validation in OpenAI and xAI providers to detect non-image file attachments
Return clear, actionable error messages suggesting Anthropic or Google for document support
Document attachment support matrix in provider guides

lib/req_llm/provider/defaults.ex: Add validate_image_only_attachments/1 helper
lib/req_llm/providers/openai.ex: Validate attachments in prepare_request(:chat, ...)
lib/req_llm/providers/xai.ex: Validate attachments in prepare_chat_request/3
guides/openai.md: Document attachment limitations
guides/xai.md: Document attachment limitations
Tests for both providers verifying image acceptance and clear error messages for non-images

Closes #317

Adds upfront validation to detect non-image file attachments and return helpful error messages before making API calls. Documents the attachment support matrix in provider guides. Closes #317 Amp-Thread-ID: https://ampcode.com/threads/T-019c117b-7aa8-72ba-9556-23dc1118034f Co-authored-by: Amp <[email protected]>

mikehostetler force-pushed the fix/317-attachment-validation branch from 48ca056 to 47314af Compare January 31, 2026 01:25

mikehostetler merged commit 00ba776 into main Jan 31, 2026
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mikehostetler deleted the fix/317-attachment-validation branch January 31, 2026 01:28