{"slug": "mcp-package-versions-in-npm-can-404-even-when-the-package-exists", "title": "MCP package versions in npm can 404 even when the package exists", "summary": "A developer at NeuraGrowth found that nine of ten pinned MCP package versions in a guide failed to resolve in the npm registry, causing 404 errors at install time even though the packages themselves exist. The fix, shipped in a commit on 2026-09-11 that changed six files, adds a verification step so every printed version pin is checked against the registry before publication. The developer notes that a non-existent pin is worse than a floating tag because it installs nothing and gives readers no clear signal why.", "body_md": "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.\n\nThe 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.\n\nA 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.\n\nThe commit that shipped on 2026-09-11 adds that verification step. Six files changed, 162 lines added, 4 removed.\n\nA 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.\n\n*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.*", "url": "https://wpnews.pro/news/mcp-package-versions-in-npm-can-404-even-when-the-package-exists", "canonical_source": "https://dev.to/robswierk/mcp-package-versions-in-npm-can-404-even-when-the-package-exists-539j", "published_at": "2026-09-17 10:00:00+00:00", "updated_at": "2026-09-17 10:23:29.330432+00:00", "lang": "en", "topics": ["agent-protocols", "developer-tools", "ai-tools"], "entities": ["NeuraGrowth", "npm", "MCP", "google-calendar-mcp"], "alternates": {"html": "https://wpnews.pro/news/mcp-package-versions-in-npm-can-404-even-when-the-package-exists", "markdown": "https://wpnews.pro/news/mcp-package-versions-in-npm-can-404-even-when-the-package-exists.md", "text": "https://wpnews.pro/news/mcp-package-versions-in-npm-can-404-even-when-the-package-exists.txt", "jsonld": "https://wpnews.pro/news/mcp-package-versions-in-npm-can-404-even-when-the-package-exists.jsonld"}}