* fix(core): mirror SEP-2243 x-mcp-header args to Mcp-Param-* on tools/call (#1846)
A strict modern (2026-07-28) HTTP server (e.g. the GitHub MCP Server)
rejects a tools/call whose argument carries an `x-mcp-header` annotation
when the matching `Mcp-Param-*` request header is missing (-32020
"header mismatch"). The Inspector never sent that header.
The SDK only mirrors inside `client.callTool()` (and skips it entirely in
a browser environment), but the Inspector routes tools/call through
`client.request()` for manual MRTR driving (#1704), so the SDK never
mirrors for us — on any transport. On top of that, the remote (web)
transport dropped per-request headers before they reached the backend's
upstream fetch.
- core/json/xMcpHeader.ts: port the SDK's non-public `buildMcpParamHeaders`
+ value encoding (Base64 sentinel for non-ASCII/whitespace/empty values)
and add `mcpParamHeadersForTool`.
- InspectorClient.attemptToolCall: on a modern connection, build the
headers from the tool's declarations + call arguments and attach them to
the tools/call request options. `Protocol.request` forwards `headers`
to the transport and preserves them across MRTR retry legs, so the
direct StreamableHTTP transport applies them. Fixes CLI/TUI.
- RemoteClientTransport.requestSend + /api/mcp/send + RemoteSendRequest:
forward per-send headers and apply them to the backend's upstream
transport.send. The browser can't set cross-origin headers, but the
Node backend can — where the Inspector's real request is issued. Fixes web.
Verified end-to-end against the live GitHub MCP Server (modern HTTP).
Closes#1846
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd
* review: harden backend header allowlist, fix breadcrumbs, trim comments
Address Copilot review on #1847:
- server.ts: restrict client-supplied per-send headers to the `Mcp-Param-`
prefix (string values only) via `mcpParamHeadersOnly` before applying them
upstream, so the per-send channel can't inject arbitrary headers (e.g.
Authorization). `settings.headers` remains the channel for configured
upstream headers. Covered by new unit tests.
- Fix stale `#1810` breadcrumbs → `#1846` in the two new tests.
- Trim the verbose mirroring comments in inspectorClient/types/remote transport.
- Drop the redundant base64-on-the-wire integration test (encoding is unit-
tested; wire delivery is proven by the verbatim test), remove two unneeded
test casts, and cover the boolean `true` branch.
Not changed (declined with reason on the PR): buildMcpParamHeaders remains a
faithful port of the SDK's helper and does not re-validate values against the
declared JSON Schema type — arg types are enforced by schema validation on
both sides, and matching the SDK's conforming wire output is the module's goal.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd
* review: mirror Mcp-Param-* on the task-augmented tools/call too
Address the maintainer review on #1847:
- `callToolStream` (the "Run as task" path) built its own request options and
never mirrored, so a task-augmented `tools/call` on an annotated tool was
still rejected by a strict modern server with -32020. It now mirrors like the
plain path.
- Extract the two blocks both `tools/call` entry points had duplicated —
`convertStringToolArgs` (the string-arg coercion) and
`applyMirroredParamHeaders` (the SEP-2243 mirroring) — so the paths can't
drift again. That duplication is why the task path was missed.
- Regression test: `callToolStream` against the modern `get_weather` server
asserts the POST carries `Mcp-Param-City` (verified failing without the fix).
- README: the modern-network showcase claimed mirroring is skipped in the
browser so the web client gets -32020, and that CLI/TUI mirror. Both are now
wrong — the Inspector mirrors itself, on every client. AGENTS: note that
xMcpHeader.ts now also builds the wire headers.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UkhhCHryVp5H3dqEnhwZ7t
* docs: correct the stale "browser omits Mcp-Param-*" copy
Both statements predate this PR and are now the opposite of true, per the
wire capture on #1847 (proxy-observed upstream headers, web leg included).
- ToolDetailPanel: the mirrored-headers note claimed the browser omits
`Mcp-Param-*`. It now says the web client's headers are applied by the Node
backend that issues the upstream request.
- createRemoteFetch: the header comment claimed an `x-mcp-header`-annotated
tool is "uncallable from the web client against a strict modern server" —
the exact wrong conclusion to reach while debugging a -32020. It now records
that the Inspector builds the headers itself, and that they do NOT travel
this `/api/fetch` proxy path: they ride the transport's per-send `headers`
through `/api/mcp/send`.
Copy only — no test asserted the old note text (ToolDetailPanel.test.tsx
matches the section title only).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UkhhCHryVp5H3dqEnhwZ7t
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: cliffhall <cliff@futurescale.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd
* Tools: x-mcp-header annotation tooling + -32602 unknown-tool rendering (#1632)
Card 9/10 of the SDK-v2 + New Spec stack. Adds SEP-2243 `x-mcp-header`
tooling to the Tools tab and adjusts result rendering for SDK v2's
unknown-tool behavior, and bumps the SDK to 2.0.0-beta.5.
- **`core/json/xMcpHeader.ts`**: a faithful port of the SDK's (non-public)
`scanXMcpHeaderDeclarations` — validates every SEP-2243 constraint
(primitive types incl. `number`, RFC 9110 token, case-insensitive
uniqueness, statically-reachable `properties`-only chain) and derives the
mirrored `Mcp-Param-{Name}` params for a kept tool.
- **Excluded tools**: the SDK silently drops tools with invalid annotations
from `tools/list`. InspectorClient now re-lists the RAW (unfiltered) list
and scans it to recompute the excluded set with reasons — gated to the
modern non-stdio era (matching the SDK's gate), recomputed on every
aggregate refresh, surfaced via a new `excludedToolsChange` event +
`getExcludedTools()` and `useInspectorClient().excludedTools`. The Tools
sidebar lists them struck-through under an "Excluded (SEP-2243)" divider
with the reason on hover.
- **Mirrored args**: ToolDetailPanel shows a "Mirrored request headers"
section listing each arg → `Mcp-Param-{Name}` (with the browser-omits note).
- **-32602 rendering**: SDK v2 rejects an unknown-tool call with `-32602`
instead of an `isError` result, which previously rendered nothing. New
ToolCallErrorPanel renders a thrown tool-call error, with a targeted
"Unknown Tool" hint for `-32602`.
Adds unit + Storybook + integration coverage (a real modern server with an
invalid-header tool fixture) for every path. `npm run ci`-equivalent checks
green.
Closes#1632
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
* test-servers: x-mcp-header modern showcase config + preset (#1632)
Register the `invalid_header_tool` fixture as a preset and add
`xmcpheader-modern-http.json` — a modern HTTP showcase serving echo, a
valid-header `get_weather`, and the invalid-header tool — so the Tools-tab
x-mcp-header tooling (mirrored headers, excluded-tools surface, -32602
rendering) can be exercised manually. Documented in the README alongside the
other per-SEP showcase configs. Smoke-tested end to end in the web client.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
* docs: add #1632 proof screenshots to pr-screenshots
End-to-end web-client verification of the x-mcp-header Tools tooling against
the modern showcase server: excluded-tools surface + reason, mirrored-headers
section, and the -32602 unknown-tool error panel.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
* Respond to review: disambiguate -32602, doc/search nits (#1632)
Addresses the review on PR #1735:
1. -32602 "Unknown Tool" mislabel: `-32602` is generic Invalid params, so a
known tool called with bad arguments hit the same code and rendered under
the definitive "Unknown Tool" heading. Replace `isUnknownToolError` with
`classifyToolCallError(code, message)` → "unknown-tool" only when the
message names it (not found / unknown tool / …), else "invalid-params"
(new "Invalid Parameters" heading + schema hint), else "generic".
2. Double pagination walk: expand the `listAllTools` comment to document that
the excluded-tools recompute is a deliberately un-cached second raw walk
(doubles list round-trips on modern non-stdio, runs even on a cache-served
aggregate) — accepted for a debugging tool, no-op on legacy/stdio.
3. Doc nit: `scanXMcpHeaderDeclarations` no longer claims to visit "$ref
targets" — reworded to note `$ref` is never followed (refs resolve into the
unreachable `$defs` body).
4. Search nit: the excluded-list filter now matches name AND title, matching
the main tools filter.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
* Tighten unknown-tool matcher to be tool-scoped (#1632 re-review nit)
The re-review noted the -32602 disambiguation was symmetric: broad markers
("does not exist", "unrecognized") could inversely mislabel a genuine
invalid-params message (e.g. "property 'region' does not exist") as "Unknown
Tool". Scope the not-found/does-not-exist family to require the word "tool" in
the same clause (matching the SDK's "Tool <name> not found"); keep "unknown
tool" / "no such tool" as standalone unambiguous markers. Adds a
tool-less-"does not exist" test asserting it classifies as invalid-params.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
* Add trigger_invalid_params showcase tool + Invalid Parameters screenshot (#1632)
Adds a `trigger_invalid_params` spec-error trigger to the modern showcase
server: the injector answers its `tools/call` with a real `-32602 Invalid
params` JSON-RPC error whose message does NOT name an unknown tool. This lets
the "Invalid Parameters" branch of the tool-call error panel (added in the
review response) be exercised live, distinct from the unknown-tool `-32602`.
- `SPEC_ERROR_TRIGGERS` gains the `trigger_invalid_params` entry (HTTP 200,
in-band -32602) + preset registration.
- Enable `injectSpecErrors` on `xmcpheader-modern-http.json` and add the tool.
- README + pr-screenshots README document it; adds the live "Invalid
Parameters" proof screenshot.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5
---------
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Sam Morrow
Cliff Hall