Protocol eras changeddocs/draft/tools/inspector/protocol-eras
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1414| `auto` | Probe `server/discover` first, and fall back to `initialize` on any non-modern outcome. |
1515| `modern` | Pin exactly `2026-07-28`. No fallback, so a non-modern server fails loudly. |
1616
17<Note>
18 **Why `legacy` is the default, and not `auto`.** A debugging tool must not
19 auto-probe. A `server/discover` probe stalls against silent legacy stdio
20 servers, and it pollutes the recorded transcript you came here to read. Opting
21 into `auto` or `modern` is a deliberate act, so what you see in the Protocol
22 tab is what your server would have seen from a client behaving the way you
23 configured.
24</Note>
17> [!NOTE]
18>
19> **Why `legacy` is the default, and not `auto`.** A debugging tool must not
20> auto-probe. A `server/discover` probe stalls against silent legacy stdio
21> servers, and it pollutes the recorded transcript you came here to read. Opting
22> into `auto` or `modern` is a deliberate act, so what you see in the Protocol
23> tab is what your server would have seen from a client behaving the way you
24> configured.
2525
2626Once connected, the negotiated era is shown as a badge on the **Protocol** tab's Messages header and in **Connection Info**. On a modern connection, `server/discover` also supplies `capabilities` (including `extensions`), `instructions`, and the list of `supportedVersions`. The server's name and version arrive in the result `_meta` under `io.modelcontextprotocol/serverInfo`.
2727
28<Frame caption="Server Settings: the Protocol Era selector, with all three choices.">
29 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/settings-protocol-era.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=34566c45f97c8af0e2c0d9ee0493b572" width="3840" height="2160" data-path="images/inspector/settings-protocol-era.png" />
30</Frame>
28
3129
3230## Reproducing each era locally
3331
from line 49
5149
5250## Logging
5351
54<Tabs>
55 <Tab title="Legacy">
56 Logging is **session-scoped**. The client sends `logging/setLevel` once, and the server emits `notifications/message` at or above that level for the rest of the session.
52**Legacy**
5753
58 The **Logs** tab shows a **Set Active Level** selector plus a **Set** button. Choose a level, click Set, and subsequent server logs stream into the panel.
54Logging is **session-scoped**. The client sends `logging/setLevel` once, and the server emits `notifications/message` at or above that level for the rest of the session.
5955
60 Reproduce with `test-servers/configs/logging-legacy-http.json`.
61 </Tab>
56The **Logs** tab shows a **Set Active Level** selector plus a **Set** button. Choose a level, click Set, and subsequent server logs stream into the panel.
6257
63 <Tab title="Modern">
64 `logging/setLevel` is **gone**. Instead the client opts in **per request**, by stamping `_meta["io.modelcontextprotocol/logLevel"]` on each outgoing request. A server MUST NOT emit `notifications/message` for a request that did not opt in.
58Reproduce with `test-servers/configs/logging-legacy-http.json`.
6559
66 The **Logs** tab therefore shows a **Log Level per Request** control instead. Pick a level and every subsequent request carries the stamp, visible in the Network tab's request body. Logs emitted while handling a request ride that request's SSE response stream.
60**Modern**
6761
68 Set the control to **Off** and the `logLevel` key is omitted entirely, so the same tool call produces no logs at all. That silence is correct behavior, not a bug.
62`logging/setLevel` is **gone**. Instead the client opts in **per request**, by stamping `_meta["io.modelcontextprotocol/logLevel"]` on each outgoing request. A server MUST NOT emit `notifications/message` for a request that did not opt in.
6963
70 The per-server default is `debug` (opted in at the most verbose level, since the Inspector is a debugging tool); set `modernLogLevel: "off"` on a server to opt back out by default.
64The **Logs** tab therefore shows a **Log Level per Request** control instead. Pick a level and every subsequent request carries the stamp, visible in the Network tab's request body. Logs emitted while handling a request ride that request's SSE response stream.
7165
72 Reproduce with `test-servers/configs/logging-modern-http.json`.
73 </Tab>
74</Tabs>
66Set the control to **Off** and the `logLevel` key is omitted entirely, so the same tool call produces no logs at all. That silence is correct behavior, not a bug.
7567
76<Frame caption="Legacy: the Logs tab offers a session-scoped Set Active Level control, and a log arrives after calling send_notification.">
77 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/logs-legacy.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=ec5fddd86d1fe7ecc1ef83549798f33e" width="3840" height="2160" data-path="images/inspector/logs-legacy.png" />
78</Frame>
68The per-server default is `debug` (opted in at the most verbose level, since the Inspector is a debugging tool); set `modernLogLevel: "off"` on a server to opt back out by default.
7969
80<Frame caption="Modern: the same tab instead offers Log Level per Request. The level is stamped on every outgoing request, and the log rides that request's stream.">
81 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/logs-modern.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=85a1d7118a1e693930aefab8ca6b21a3" width="3840" height="2160" data-path="images/inspector/logs-modern.png" />
82</Frame>
70Reproduce with `test-servers/configs/logging-modern-http.json`.
8371
72
73
74
75
8476***
8577
8678## Resource subscriptions
8779
88<Tabs>
89 <Tab title="Legacy">
90 Clicking **Subscribe** on a resource sends `resources/subscribe`. The Subscriptions section lists the URI with no stream chrome. When the resource changes, the server emits `notifications/resources/updated` and the subscribed tile's last-updated time is stamped.
80**Legacy**
9181
92 Reproduce with `test-servers/configs/subscriptions-legacy-http.json`, which also serves an `update_resource` tool so you can drive the notification round-trip yourself.
93 </Tab>
82Clicking **Subscribe** on a resource sends `resources/subscribe`. The Subscriptions section lists the URI with no stream chrome. When the resource changes, the server emits `notifications/resources/updated` and the subscribed tile's last-updated time is stamped.
9483
95 <Tab title="Modern">
96 The same **Subscribe** button instead sends **`subscriptions/listen`**, with a filter carrying `resourceSubscriptions` plus whichever `*ListChanged` opt-ins apply (such as `resourcesListChanged`). The subscription is confirmed when the server sends `notifications/subscriptions/acknowledged`.
84Reproduce with `test-servers/configs/subscriptions-legacy-http.json`, which also serves an `update_resource` tool so you can drive the notification round-trip yourself.
9785
98 Because the subscription is now a long-lived stream rather than a session flag, the Subscriptions section grows a **stream-status badge** in its header that moves from `Connecting...` to `Listening`. If the stream drops, the badge shows `Reconnecting...` while the Inspector re-sends `subscriptions/listen`. It shows `Stream ended` once the stream closes for good. It shows `Not acknowledged` when the server answers the listen with a plain result and never sends the acknowledgement; the Inspector does not retry in that case.
86**Modern**
9987
100 Reproduce with `test-servers/configs/subscriptions-modern-http.json`. To see the `Not acknowledged` state, use `test-servers/configs/subscriptions-never-acknowledged-http.json`. That server acknowledges your first subscription, then refuses every later listen, so subscribing to a second resource trips the badge.
101 </Tab>
102</Tabs>
88The same **Subscribe** button instead sends **`subscriptions/listen`**, with a filter carrying `resourceSubscriptions` plus whichever `*ListChanged` opt-ins apply (such as `resourcesListChanged`). The subscription is confirmed when the server sends `notifications/subscriptions/acknowledged`.
10389
104<Frame caption="A modern subscription: the Subscriptions section carries a LISTENING stream-status badge that a legacy subscription has no need for.">
105 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/resources-subscriptions-modern.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=5ca4c64c6783eb210fe54248f03de144" width="3840" height="2160" data-path="images/inspector/resources-subscriptions-modern.png" />
106</Frame>
90Because the subscription is now a long-lived stream rather than a session flag, the Subscriptions section grows a **stream-status badge** in its header that moves from `Connecting...` to `Listening`. If the stream drops, the badge shows `Reconnecting...` while the Inspector re-sends `subscriptions/listen`. It shows `Stream ended` once the stream closes for good. It shows `Not acknowledged` when the server answers the listen with a plain result and never sends the acknowledgement; the Inspector does not retry in that case.
10791
92Reproduce with `test-servers/configs/subscriptions-modern-http.json`. To see the `Not acknowledged` state, use `test-servers/configs/subscriptions-never-acknowledged-http.json`. That server acknowledges your first subscription, then refuses every later listen, so subscribing to a second resource trips the badge.
93
94
95
10896***
10997
11098## Tasks
from line 99
11199
112100Tasks change the most between protocol eras, including *how the Inspector UI tab is gated*.
113101
114<Tabs>
115 <Tab title="Legacy">
116 The **Tasks** tab appears when the server advertises `capabilities.tasks`. Run a tool with **Run as task** enabled and the tab lists it, populated by `tasks/list` and polled with `tasks/get`. The completed payload is fetched with a **blocking `tasks/result`**, and **Cancel** sends `tasks/cancel`.
102**Legacy**
117103
118 Reproduce with `test-servers/configs/tasks-legacy-http.json`.
119 </Tab>
104The **Tasks** tab appears when the server advertises `capabilities.tasks`. Run a tool with **Run as task** enabled and the tab lists it, populated by `tasks/list` and polled with `tasks/get`. The completed payload is fetched with a **blocking `tasks/result`**, and **Cancel** sends `tasks/cancel`.
120105
121 <Tab title="Modern">
122 Tasks are an **extension** (`io.modelcontextprotocol/tasks`, [SEP-2663](/seps/2663-tasks-extension)), so the tab is gated on the server *advertising that extension* rather than on `capabilities.tasks`.
106Reproduce with `test-servers/configs/tasks-legacy-http.json`.
123107
124 Run a tool as a task and `tools/call` returns a `CreateTaskResult` (`resultType: "task"`, visible in the Protocol and Network tabs). The Inspector polls **`tasks/get`** only; there is no `tasks/list`, so **Refresh** re-polls the handles the client already knows about. A completed task **inlines its result**, with no blocking `tasks/result` call.
108**Modern**
125109
126 A task that needs more information moves to `input_required` and surfaces an embedded [elicitation](/specification/draft/client/elicitation) in the pending-request modal (the dialog the web client opens whenever a request is waiting on you). Answering it sends **`tasks/update`** carrying the `inputResponses`, and the next poll completes.
110Tasks are an **extension** (`io.modelcontextprotocol/tasks`, [SEP-2663](/seps/2663-tasks-extension)), so the tab is gated on the server *advertising that extension* rather than on `capabilities.tasks`.
127111
128 Reproduce with `test-servers/configs/tasks-modern-http.json` (tools `modern_task` and `modern_input_task`).
129 </Tab>
130</Tabs>
112Run a tool as a task and `tools/call` returns a `CreateTaskResult` (`resultType: "task"`, visible in the Protocol and Network tabs). The Inspector polls **`tasks/get`** only; there is no `tasks/list`, so **Refresh** re-polls the handles the client already knows about. A completed task **inlines its result**, with no blocking `tasks/result` call.
131113
132<Frame caption="Legacy: the Tasks tab is populated from tasks/list, and the payload is fetched with a blocking tasks/result.">
133 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/tasks-legacy.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=777729bfc1b58b359808c8120d9597d3" width="3840" height="2160" data-path="images/inspector/tasks-legacy.png" />
134</Frame>
114A task that needs more information moves to `input_required` and surfaces an embedded [elicitation](/specification/draft/client/elicitation) in the pending-request modal (the dialog the web client opens whenever a request is waiting on you). Answering it sends **`tasks/update`** carrying the `inputResponses`, and the next poll completes.
135115
136<Frame caption="Modern: the client polls tasks/get on handles it already holds, and the completed task inlines its result; note resultType: complete in the full task object.">
137 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/tasks-modern.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=8e90d128528463fd672537c79db2e1fe" width="3840" height="2160" data-path="images/inspector/tasks-modern.png" />
138</Frame>
116Reproduce with `test-servers/configs/tasks-modern-http.json` (tools `modern_task` and `modern_input_task`).
139117
118
119
120
121
140122***
141123
142124## Multi-round tool results (MRTR)
from line 139
157139| `mrtr_empty` | One elicitation round, then completes with an empty result (no `content`, no `structuredContent`). |
158140| `mrtr_loop` | Never completes, so the client stops at its `MRTR_MAX_ROUNDS` limit. |
159141
160<Note>
161 The legacy pattern of a server calling `server.elicitInput` (the test servers'
162 `collect_elicitation` preset) **errors** on a 2026-07-28 connection, because
163 server-to-client requests aren't allowed there. MRTR is its modern
164 replacement.
165</Note>
142> [!NOTE]
143>
144> The legacy pattern of a server calling `server.elicitInput` (the test servers'
145> `collect_elicitation` preset) **errors** on a 2026-07-28 connection, because
146> server-to-client requests aren't allowed there. MRTR is its modern
147> replacement.
166148
167<Frame caption="An MRTR round paused at the pending-request modal, tagged input_required. Answering it retries the original request.">
168 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/mrtr-pending-request.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=99f8acb7f845a12aed42bcea4d310fee" width="3840" height="2160" data-path="images/inspector/mrtr-pending-request.png" />
169</Frame>
149
170150
171<Frame caption="The monitoring sidebar's Protocol tab after mrtr_confirm completes. Both tools/call rounds sit inside one MRTR conversation, Round 1 tagged input_required and Round 2 complete, while unrelated traffic stays outside it.">
172 <img src="https://mintcdn.com/mcp/pUebPdrb6PY5_mfH/images/inspector/mrtr-protocol-conversation.png?fit=max&auto=format&n=pUebPdrb6PY5_mfH&q=85&s=b083d8127a7a67028fcd9702b25aeac1" width="3840" height="2160" data-path="images/inspector/mrtr-protocol-conversation.png" />
173</Frame>
151
174152
175153***
176154
from line 163
185163
186164Reproduce with `test-servers/configs/xmcpheader-modern-http.json`.
187165
188<Note>
189 On a modern connection the Inspector mirrors `x-mcp-header` arguments into
190 `Mcp-Param-*` headers itself, in all three clients. In the **web** client the
191 headers are added by the Inspector's Node backend, which issues the upstream
192 request, so they reach the server even though the browser never sends them.
193</Note>
166> [!NOTE]
167>
168> On a modern connection the Inspector mirrors `x-mcp-header` arguments into
169> `Mcp-Param-*` headers itself, in all three clients. In the **web** client the
170> headers are added by the Inspector's Node backend, which issues the upstream
171> request, so they reach the server even though the browser never sends them.
194172
195<Frame caption="get_weather shows its mirrored city -> Mcp-Param-City header, and the Network sidebar confirms the call carried mcp-param-city: Boston. invalid_header_tool is struck through under the Excluded (SEP-2243) divider.">
196 <img src="https://mintcdn.com/mcp/pUebPdrb6PY5_mfH/images/inspector/tools-sep2243.png?fit=max&auto=format&n=pUebPdrb6PY5_mfH&q=85&s=0e011c3012332c0a74d0f57fc84a5cf2" width="3840" height="2160" data-path="images/inspector/tools-sep2243.png" />
197</Frame>
173
198174
199175### `-32602` error panels
200176
from line 199
223199| `trigger_unsupported_version` | `400` | `-32022` | Unsupported version; supported versions in `data.supported`. |
224200| `trigger_method_not_found` | `404` | `-32601` | Method not found. |
225201
226<Frame caption="The Network tab shows the HTTP layer; here, the 400 Bad Request the strict server answered with.">
227 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/network-modern-headers.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=7df4c01f5ab68aa7632ac3b5a5866b42" width="3840" height="2160" data-path="images/inspector/network-modern-headers.png" />
228</Frame>
202
229203
230<Frame caption="The Protocol tab renders the same failure as a typed spec error: -32022 UnsupportedProtocolVersion, with the versions the server does support.">
231 <img src="https://mintcdn.com/mcp/gk28X8wi_tbRYzej/images/inspector/protocol-modern-error.png?fit=max&auto=format&n=gk28X8wi_tbRYzej&q=85&s=d578ea8262ff327e4d61d3697937900b" width="3840" height="2160" data-path="images/inspector/protocol-modern-error.png" />
232</Frame>
204
233205
234206***
235207
No line in this hunk matches that.