Was wiring a filesystem MCP into Cursor so the agent could peek at configs.
Asked it to "check the project layout". It ran what looked like a recursive ls and dumped ~40k tokens of node_modules paths into the chat. Context window was basically toast after one tool call.
I ended up adding a .mcpignore with node_modules, .git, dist. Works now, but curious — is everyone hand-rolling ignore lists, or is there a sane default I'm missing?
Left Claude Code running against our staging MCP last night so it could finish a migrations cleanup. Woke up to Anthropic showing $41 in overnight usage. Turns out the access token had rotated at 2am…
Spent Friday afternoon debugging why Claude Desktop kept dropping my custom MCP server mid session. Turns out the OAuth refresh token expired after 55 minutes, the client just stopped calling tools w…
War story from last night, maybe useful if you wire custom MCP tools into Cursor. I built a tiny MCP server that exposes prisma schema + db sample so the agent can read my Next.js app's schema withou…
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hand-rolling ignore lists here too. mine started as node_modules + .git and somehow grew into a 40-line poem of dist/, coverage/, .next, storybook-static…
one thing that helped: wrap the MCP so
listrefuses anything under those paths before the model even sees a response. otherwise it will politely ask for “just one more folder”.same. default recursive tools are a footgun on any JS repo. i wrap the MCP with max-depth=2 and a denylist before it touches the model. if your server cannot refuse a path, the model will eventually ask for it.
denylist is necessary but not enough on monorepos. i had max-depth=2 and it still burned ~12k tokens walking
packages/*/node_modulesvia symlink hops.now i only expose an allowlist of absolute paths. boring. cheaper.
hit this friday. agent then helpfully tried to read package-lock.json in 200-line chunks. i just uninstalled the filesystem MCP and pointed it at a single docs folder via a tiny custom server. less magic, way less bill shock.
same escape hatch. custom server that only serves
./docsand./.cursor/rules. agent still asked for../secrets.envonce — server returned path_not_allowed and it finally stopped.if yours has no deny semantics, uninstall is the right call.