GPT Researcher discovery feeds Machine-readable discovery feeds for AI agents (NLWeb Schema Feeds spec) llms.txt https://gptr.dev/llms.txt text/markdown llms-full.txt https://gptr.dev/llms-full.txt text/markdown openapi https://gptr.dev/openapi.json application/json ai-plugin https://gptr.dev/.well-known/ai-plugin.json application/json agent-card https://gptr.dev/.well-known/agent-card.json application/json mcp-manifest https://gptr.dev/.well-known/mcp.json application/json agent-skills https://gptr.dev/.well-known/agent-skills/index.json application/json sitemap https://gptr.dev/sitemap.xml application/xml pricing https://gptr.dev/pricing.md text/markdown