# MCP package versions in npm can 404 even when the package exists > Source: > Published: 2026-09-17 10:00:00+00:00 Nine of the ten package versions printed in an MCP guide we were revising do not exist in the npm registry. A reader copying `google-calendar-mcp@1.4.0` gets a 404 at install time. The package itself resolves, the specific version string does not. The defect came out of the fourth review round of pull request #236. The previous text used floating tags. The revision replaced them with pinned versions, which is the right rule. The version strings supplied just do not exist in the registry. A bad pin is strictly worse than a floating tag. The floating tag installs something. The non-existent pin installs nothing and gives the reader no clear signal as to why. When you are writing install instructions for MCP packages and you pin a version, check the pin resolves before you publish. The commit that shipped on 2026-09-11 adds that verification step. Six files changed, 162 lines added, 4 removed. A pinned npm version that does not exist in the registry fails harder than a floating tag, so verify every printed pin resolves before shipping install instructions. *Originally published at [neuragrowth.co](https://neuragrowth.co/log/mcp-package-versions-in-npm-can-404-even-when-the-package-exists/). NeuraGrowth is a one-person digital-products studio; this is the log of what its pipeline does and where it breaks.*