MCP compatibility

Conduit has one policy, audit, registry, and dispatcher. Its native public profile is MCP 2026-07-28 (server/discover, tools/list, and terminal JSON tools/call). At ingress only, it also adapts the standard session-based Streamable HTTP negotiation used by current desktop and CLI MCP clients. The adapter never changes the modern protocol used to communicate with downstream servers.

Compatibility matrix

Client / mode	Status	Negotiation accepted	Last verified
MCP Inspector 2.4.0, default	Supported	`initialize` + session, `2025-11-25`	Real `tools/list` and `tools/call` through Conduit on 2026-09-02.
MCP Inspector 2.4.0, `protocolEra: modern`	Supported	Native `server/discover`, `2026-07-28`	Real `tools/list` and `tools/call` on 2026-09-02.
Claude Code 2.1.236, HTTP MCP	Supported	Standard session-based Streamable HTTP (`2025-11-25`)	`claude mcp get` reported `Connected` on 2026-09-02. An authenticated Claude conversation is required to issue a tool call.
Codex CLI 0.149.1 remote MCP	Supported	Standard session-based Streamable HTTP (`2025-06-18`)	The real Codex connector completed MCP initialization/event-channel setup on 2026-09-02. A logged-in Codex session is required for model-directed tool calls.
Older/other standard clients	Conditional	Exactly `2025-06-18` or `2025-11-25`, `initialize`, `Mcp-Session-Id`	Try the standard Streamable HTTP endpoint; unsupported protocol versions fail closed.
stdio, SSE-only, OAuth broker clients	Unsupported	—	Conduit is an HTTP gateway, not a stdio/SSE/OAuth broker.

The verification dates describe installed-client interoperability, not a claim that a client vendor will never change its wire behavior. Keep Conduit and the client updated together and use the regression tests when upgrading either.

What the adapter accepts

For a standard client, Conduit accepts initialize with protocol version 2025-06-18 or 2025-11-25, returns an opaque Mcp-Session-Id, accepts the client's notifications/initialized, and requires that same session/version pair on later tools/list and tools/call requests. Sessions are opaque, per-client, version-bound, and removed by DELETE /mcp; they are never passed to a downstream or used to select a route.

GET /mcp for a valid standard session returns a short comment-only text/event-stream response. It exists for clients that establish their notification channel during initialization. Conduit never turns a downstream tool response into SSE and does not emit progress, subscriptions, tasks, or server notifications. Tool results remain terminal JSON.

All adapted tools/list and tools/call requests continue through the exact same registry snapshot, deny-wins policy, header validation, durable audit-before-dispatch write, credential isolation, route lookup, timeout, and one-shot downstream dispatch as native modern requests. The adapter supplies only the internal Mcp-Name correlation header from the validated JSON body; a caller-provided conflicting value is rejected.

Downstream terminal SSE responses

Conduit supports Streamable HTTP downstreams that return either application/json terminal JSON-RPC responses or a finite text/event-stream response containing exactly one correlated terminal JSON-RPC message event. The SSE decoder is incremental and bounded by the same catalog or tool-response limit as JSON. It supports LF/CRLF framing, comments, chunk boundaries, and multiple data: lines joined according to SSE framing rules.

This is terminal-response compatibility, not a streaming bridge. Conduit does not forward downstream SSE to clients, relay progress/events, accept unrelated or multiple terminal messages, reconnect/replay, or retry a tools/call. A malformed, truncated, mismatched, oversized, progress-style, or indefinite stream fails closed. Once a tool call may have reached its downstream, a lost or unreadable terminal response remains an uncertain outcome.

Stateful downstream tool calls may return Mcp-Session-Id; Conduit performs at most one bounded cleanup DELETE using that invocation-owned downstream session ID. It does not retain or replay that identifier on a later invocation. A session advertised before a failed, oversized, or disconnected response is still cleaned up where the downstream made that identifier available.

Client setup

Start Conduit and wait for "ready": true first:

conduit --config conduit.yaml
curl -sS http://127.0.0.1:8080/healthz

Claude Code

claude mcp add --transport http conduit http://127.0.0.1:8080/mcp
claude mcp list

For project configuration use --scope project; Claude Code requires project MCP approval before it opens the connection. claude mcp get conduit should show Status: Connected. Then use the namespaced tools in an authenticated Claude Code conversation, for example github.add or calc.square.

Codex CLI / Codex app

codex mcp add conduit --url http://127.0.0.1:8080/mcp
codex mcp list

Start a logged-in Codex session and ask it to use a namespaced Conduit tool. The remote MCP configuration is HTTP; do not configure Conduit as a stdio server. A 401 from the OpenAI model endpoint is Codex authentication failure, not a Conduit MCP protocol failure.

MCP Inspector default mode

npx @modelcontextprotocol/inspector --cli \
  --transport http --server-url http://127.0.0.1:8080/mcp \
  --method tools/list --format json

To call a tool:

npx @modelcontextprotocol/inspector --cli \
  --transport http --server-url http://127.0.0.1:8080/mcp \
  --method tools/call --tool-name calc.square \
  --tool-args-json '{"value": 9}' --format json

MCP Inspector forced-modern mode

Save inspector-modern.json:

{
  "mcpServers": {
    "conduit": {
      "type": "http",
      "url": "http://127.0.0.1:8080/mcp",
      "protocolEra": "modern"
    }
  }
}

Then run:

npx @modelcontextprotocol/inspector --cli \
  --config inspector-modern.json --server conduit \
  --method tools/list --format json