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Make complex _meta possible #1910
Description
Is your feature request related to a problem? Please describe.
For my use cases i need to be able to attach complex (json) _meta to mcp requests. With the current implementation only <string,string> pairs are possible.
Describe the solution you'd like
Replace (maybe optionally) the string, string pair list of _meta in the server settings with a json editor.
Describe alternatives you've considered
I had already implemented this behaviour for v1 and opened a PR (#1159)
Additional context
Since you are no longer accepting direct contributions, i will not open a PR for it, but please consider adding this functionality.
There is nothing in the MCP spec which restricts custom _meta data to just string,string pairs so i don't think the main mcp testing tool (which the inspector is for many people) should do that.
Activity
docs: add the six-month Inspector roadmap (Aug 2026 → Feb 2027)
fix: drop a schema-invalid `_meta.progressToken` instead of sending it
fix: redact secrets nested inside metadata in `servers/show`
fix(web): update a fixture the merge brought in to the object metadat…
fix: validate every reserved `_meta` member against the SDK's own schema
cliffhall commentedon Aug 24, 2026
Shipped in #2094 (merge commit b44c090 on
v2/main)._metavalues may now be any JSON — objects, arrays, numbers, booleans,null— across core, web, TUI and CLI. Server Settings → Request Metadata is a JSON editor (Ace: code folding, brace auto-closing, per-line error annotation) instead of key/value rows, which structurally could not express an object value.Your existing
mcp.jsonkeeps working: the pre-existing[{ "key", "value" }]pair array is still read, and is rewritten as an object the next time the Inspector saves that entry.Two caveats worth knowing:
progressToken(a string or a safe integer) andio.modelcontextprotocol/related-task({ "taskId": "<string>" }). A reserved key whose value does not match is dropped from the request, because a conforming server rejects the entire request over one bad reserved member.1e400(which parses toInfinityand would be sent asnull) is refused with an inline message rather than silently transmitted.Thanks for the report — and for the v1 prototype in #1159, which made the intended UX unambiguous.
Merge branch 'v2/main' into v2/fix/2067-proxy-undici
feat: allow complex JSON values in request _meta
fix(mcpi): restore build after v2/main merge