Free vs paid documentation MCP servers freshness is the product.

Free documentation servers come in two flavors. Local ones, like dash-mcp-server, search docsets already on your machine — zero network dependency, but the docsets update only when you do. Hosted free ones, Context7 being the canonical example, maintain the index for you and have become near-default attachments for coding agents.

Vendor-run servers are a third flavor: webcomponents-react-mcp-server and Ignite UI MCP Server exist because the vendor benefits when agents generate correct code against their framework. The docs service is marketing that happens to be useful.

A free hosted docs index has no revenue tied to its uptime or freshness. If the maintainer loses interest, the index quietly goes stale — and a stale docs server is worse than none, because the agent trusts it. Rate limits are the other pressure: popular free endpoints throttle under load precisely when usage proves their value.

Self-hosting an open-source docs server fixes control but transfers the indexing burden to you, which for fast-moving frameworks is a recurring chore, not a one-time setup.

Niche, high-stakes documentation is where paying per lookup is rational. Servers like Unreal Engine API Documentation and Unity API Documentation pitch a precise promise — no hallucinated C++ signatures or includes — and one wrong signature costs a developer more debugging time than thousands of $0.01 lookups. The RevoGrid pair shows the emerging shape: a standard hosted tier alongside a Pro one with deeper guidance.

The billing unit is obvious here: one query, one answer, one price.

x402 was practically made for this category. A docs lookup is small, frequent, and valuable in cents, not dollars — exactly the micropayment range. The agent receives an HTTP 402 with the price, pays in USDC on Base (settled in ~2 seconds), and gets the answer, with a signed Ed25519 receipt and no signup or API key anywhere in the loop.

That lets a maintainer of a specialized index — CesiumJS internals, a 3D SDK like Sceneview — charge from $0.01 per lookup and fund the freshness that makes the index worth querying.

Mainstream framework? Free hosted indexes like Context7 cover you well. Vendor framework? Use the vendor's own server — they have the strongest incentive to keep it correct. Niche or version-critical APIs? A paid per-lookup endpoint with a maintainer whose income depends on accuracy is the safest bet. All 84 live options sit side by side in Loomal's Documentation Access category.