Fix: Startup banner corrupts stdio JSON-RPC stream#8
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Jul 4, 2026
Fix: Startup banner corrupts stdio JSON-RPC stream
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Summary
When starting up Claude desktop which also starts the MCP server at the same time, the MCP server fails to connect when using the npx method, throwing:
Unexpected token '◇', "◇ injected"... is not valid JSONRoot cause
Looking at the
package.json, the json declared"dotenv": "", which is an empty version range that floats to the latest dotenv on every fresh install. Fresh installs (e.g. npx -y @programcomputer/nasa-mcp-server@latest) resolve dotenv v17+, which prints a startup banner to stdout by default:◇ injected env (1) from .env // tip: ...A stdio MCP server uses stdout exclusively as its JSON-RPC channel, so this banner corrupts the stream and the client fails to parse the handshake. The committed lockfile pinned the older, silent dotenv 16.4.7, which masked the issue in local development.
Changes
dotenvto^17.2.0so the version no longer silently floats.quiet: trueto everydotenv.config()call to suppress the v17 banner:src/utils/api-client.ts(4 calls) — imported byindex.ts, so its top-level calls run at startup and were the primary culpritsrc/index.ts(1 call)src/utils/env-setup.ts(4 calls)Verification
I have locally built the updated source code and piped a MCP
initializerequest intodist/index.jswith a.envpresent and verified that the error message does not appear when starting Claude.