Field notes on AI-native SaaS.
How to ship MCP servers, embed in-product AI assistants, and monetize AI usage — written by the team building the platform.
- MCP education
How does AI function calling and tool execution work?
The model never executes anything: it emits JSON, your code runs the tool, and you append the result and call the model again. The full loop in 20 lines, plus the five failure modes that only show up in production.
Sep 28, 2026 · 8 min - MCP education
isError is not an error: how an MCP tool fails and still looks successful
The MCP isError flag rides inside a successful JSON-RPC response, which is why hosts miss it. Three production bugs from our gateway: the failure a host has no name for, HTTP 200 with a GraphQL errors array, and the null result that isn't an error at all.
Sep 18, 2026 · 7 min - MCP education
Intercom's MCP server: two regions and a registration endpoint that says no
Intercom runs separate MCP hosts for US and EU workspaces, still answers on its deprecated /sse path, uses the older OAuth discovery pattern and rejects dynamic client registration. Measured against the live endpoints.
Sep 16, 2026 · 7 min - MCP education
Slack's MCP server is live. Your users still can't connect their own workspace.
Slack's MCP server uses user tokens, supports PKCE and returns a spec-correct 401. It also has no registration endpoint, and Slack permits MCP only for Marketplace-listed and internal apps. What that means if you embed an assistant in someone else's product.
Sep 15, 2026 · 7 min - MCP education
MCP Tools vs Resources vs Prompts: which primitive when
MCP exposes three primitives because hosts render each as a different UI. Here's the decision rule for picking Tools, Resources, or Prompts — with examples.
Jun 27, 2026 · 4 min - MCP education
What is an MCP server? A plain-English guide for 2026
Plain-English guide to MCP servers: what the Model Context Protocol is, how an MCP server differs from a REST API, the anatomy of tools and resources, and a production checklist.
Jun 25, 2026 · 6 min - MCP education
OAuth for MCP servers: the 2025-06 spec, explained
OAuth 2.1 with PKCE is how the MCP spec authorizes remote servers. Here's the flow, the spec requirements, and the pitfalls to avoid when shipping a hosted MCP server.
Jun 23, 2026 · 5 min - MCP education
MCP vs function calling: what's actually different
MCP and function calling solve different problems. Function calling is a per-model capability; MCP is the cross-model protocol that makes your tools portable. Here's how they fit together in production.
Jun 22, 2026 · 5 min