Problemsby IbisModel Context Protocol fails to return valid structured output
LLM apps5 posts from 5 people3d active+11 post in the last 7 days, 3 the 7 days before (fading)
Posts per day
The posts behind it
5, newest firstfeat(tools): native Model Context Protocol (MCP) client support (SSE and stdio tool discovery)...Slack, Notion, etc.) with a single endpoint URL. --- ### Architectural Diagram: Current Workarounds vs. Native MCP Client #### Current Limitation (High Friction): #### Proposed Native Architecture: --- ### Technical Specification & Implementation Plan #### 1. Backend MCP Client...open-webui/open-webui · claytontavaresdan2 repliesOpen ↗feat: Admin-configured, opt-in citation mapping for MCP / tool-server results...The model uses this text in its answer, but the message has no sources. The existing workaround is for the MCP server to call `POST /api/v1/chats/{chat_id}/messages/{message_id}/event` with an Open WebUI API key (see the maintainer's reply in #25174). That forces every MCP...open-webui/open-webui · JaimeArboleda1 reactions, 2 repliesOpen ↗[BUG] JSON Schema field constraints (pattern/minimum/...) silently dropped on nullable list-form type fields### Description When a tool/MCP JSON Schema uses the list-form nullable type `{"type": ["string", "null"]}` (or `["integer","null"]`, etc.), CrewAI's `create_model_from_schema` builds a Pydantic field but **silently drops every field constraint**. In...crewAIInc/crewAI · linhongyu510Open ↗I revived HTTP 402: An MCP server where AI agents autonomously pay for data using Base USDC....standard scraping tools break. . I built an MCP server that uses LLMs to perfectly map messy DOMs to strict JSON schemas, but I added an experimental payment layer: **Native HTTP 402 Payment Required**. . Instead of you putting your Stripe card down for an API key, your...r/LangChain · u/Puzzleheaded_Pop2019Open ↗[BUG] MCPServerAdapter sends JSON null for every unset optional tool argument, breaking strict-schema MCP servers...was correctly left unset by the caller. This looks like a regression of #302 ("Agent unable to handle optional parameters for mcp server"), which was closed in 2025 after a fix landed in `mcpadapt>=0.1.9`. That fix was in `mcpadapt`'s model-generation code. Since then,...crewAIInc/crewAI · shiqi446-blip3 repliesOpen ↗
Companies and products named
About this problem
Evidence
5 posts from 5 people in 3 places, about 3 a week over 11 days. Mostly on open-webui/open-webui, crewAIInc/crewAI, r/LangChain. Tools named alongside: CrewAI, Open WebUI, LangChain, Vercel.
Frustration Frustration 0 of 3· Seen on GitHub issues, Reddit
How it was grouped
Posts that state a pain and match the "structured-output" rule about Model Context Protocol. First post Oct 5, 2026, latest Oct 15, 2026. Corroborated: 3 or more posts from 2 or more people or places. Method
The same problem elsewhere
Models fail to return valid structured outputClaude fails to return valid structured outputLlamaIndex fails to return valid structured outputOpenAI fails to return valid structured outputCodex fails to return valid structured outputOllama fails to return valid structured outputAnthropic fails to return valid structured outputMistral fails to return valid structured outputQwen fails to return valid structured outputClickHouse fails to return valid structured output
Other Model Context Protocol problems
Model Context Protocol tables suffer from small files and skewModel Context Protocol users keep filing bugsModel Context Protocol upgrades break working setupsTrouble with Model Context Protocol serverModel Context Protocol rate limits and usage caps block workTrouble with Model Context Protocol reportsModel Context Protocol vulnerabilities are hard to triage and patchTrouble with Model Context Protocol sessionTrouble with Model Context Protocol clientModel Context Protocol login, SSO or OAuth breaksModel Context Protocol compute costs spiral out of controlModel Context Protocol gives confidently wrong answers
History
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Model Context Protocol fails to return valid structured output (3 posts)