Inspect MCP Transports

Use /mcp or /mcp status to inspect attached MCP servers in detail. Use /mcp list for the shorter configured-and-attached inventory.

Protocol era and transport are separate concepts. A remote Streamable HTTP endpoint can negotiate modern or legacy protocol behavior; a legacy protocol connection is not necessarily the configured legacy SSE transport.

`/mcp` label	Meaning	Display difference
`(modern)`	Automatic negotiation selected the discovery-era protocol.	Session, legacy Health, and ping columns are omitted.
`(legacy)`	Automatic negotiation selected the initialization-era protocol.	Session and legacy Health are shown.
`(forced modern)` / `(forced legacy)`	`protocol_mode` was explicitly selected for interoperability testing or debugging.	Uses the corresponding modern or legacy display.

auto is the default and should be preferred for normal connections. To test a server's legacy compatibility path, connect with --protocol legacy; forcing a mode changes client negotiation behavior, not the HTTP transport.

Modern remote MCP: JSON, SSE, and progress

This recording connects to Hugging Face's MCP Server, calls hf_whoami for a direct JSON response, then generates an image over SSE. The image call receives progress notifications and renders the result before /mcp opens. The diagnostic timeline distinguishes direct JSON-RPC messages from SSE streams and shows request, response, and notification activity. The LISTEN (SSE) channel is disabled because the server does not advertise list-change notifications or resource subscriptions.

The command leaves protocol selection at its default, auto. Fast-agent discovers the server's supported modern protocol and /mcp reports the negotiated result:

protocol  2026-07-28 (modern)

The modern display intentionally omits the legacy Session and Health fields, and its channel timeline has no legacy ping column. The identity lookup appears on POST (JSON). The image request and its progress notifications appear on POST (SSE), both during execution and as notification activity in the subsequent transport display.

Legacy remote MCP: session and health

This deterministic recording connects to a local legacy Streamable HTTP fixture. The server returns a fixed MCP-Session-Id; one-second health pings establish a visible healthy state before /mcp opens its 60-segment timeline.

For a forced legacy connection, /mcp shows the initialization-era protocol, the observed HTTP session identifier, and legacy health state:

protocol  2025-11-25 (forced legacy)
session   docs-legacy-session
health    ok

forced legacy means the client was configured with protocol_mode: legacy. The Session value is an observed MCP-Session-Id response header. Health and ping information belong to the legacy client path; their absence from the modern display is intentional.

Reading the `/mcp` display

Implementation, protocol, and session

The first lines identify the server implementation, version, client, and negotiated protocol era. A forced mode is shown as (forced modern) or (forced legacy). The protocol label reports the negotiated result rather than printing internal negotiation steps separately.

Successful negotiation requests are included in mcp calls: alongside normal operations. Modern negotiation records discover; legacy negotiation records initialize. Forced-modern connections still send server/discover so capabilities and metadata are available, but they fail rather than falling back to legacy initialization when discovery is rejected. Reconnecting repeats and counts the corresponding negotiation request.

mcp calls: discover:1, list_tools:1, tool:2

For modern-era connections, /mcp omits Session and legacy Health fields. Non-modern displays include Session; it contains the observed MCP-Session-Id, or None when no session header was captured. The local value for stdio describes transport locality, not a protocol session.

Transport channel history

Transport activity is shown only when fast-agent has a live diagnostics source. Public httpx hooks classify outgoing Streamable HTTP requests, responses, resumptions, and errors without consuming response bodies or streamed SSE events.

POST (JSON) and POST (SSE) classify observed POST responses by their Content-Type. LISTEN (SSE) is the separate server-event listening channel. These labels describe live HTTP behavior; they do not mean the server was configured with the legacy SSE transport.

Timeline symbols prioritize significant events in this order:

error → disabled/request → response → notification/ping → none

When several events land in one segment, the higher-priority state remains visible.

Server capabilities

To, Pr, Re: Tools, Prompts, and Resources. A highlighted token indicates list-change notifications.
Rs: Resource subscriptions.
Lo, Co: Logging and completions.
Ex: Experimental capabilities.
In: Server instructions. Warning and error colors indicate instructions that are available but not injected into the agent system prompt, or disabled.

Extensions and client settings

Sk: SEP-2640 Skills Extension Draft (d7490ecd) support. It does not indicate compatibility with legacy index/archive skill servers.
Ui: Detected MCP Apps or OpenAI Apps SDK configuration.
Ro: Roots offered to the MCP server.
El: Elicitation mode.
Sa: Sampling mode.
Sp: Client-name spoofing.

Provider-managed MCP does not use fast-agent's MCP client, so these local negotiation and transport diagnostics do not apply to provider-owned connections.

Diagnostics configuration

Configure timeline density in fast-agent.yaml:

mcp:
  diagnostics:
    enabled: true
    timeline:
      steps: 60
      step_seconds: 1

steps controls the number of rendered segments and step_seconds controls the duration represented by each segment. Set mcp.diagnostics.enabled to false to disable MCP diagnostics collection.