Allows management of tmux sessions, including creating, monitoring, and controlling long-running jobs. Provides tools to list sessions, capture pane output, send keystrokes, and kill sessions.
Lets Claude Desktop on Linux start, monitor, and control long-running jobs inside tmux sessions. Designed for ML training, data pipelines, and anything else you want to survive beyond a single conversation.
Claude can start a detached training run, check on it an hour later by capturing the last N lines of its pane, send keystrokes (including Ctrl+C), and kill the session when done. You can tmux attach -t <name> from any real terminal to watch the same session live — Claude and a human can observe simultaneously.
Linux with tmux installed:
sudo apt install tmuxWorks with the default per-user tmux server (no shared-server setup needed).
Related MCP server: Tmux MCP Server
Download the latest Sessions.mcpb from the Releases page.
In Claude Desktop: Settings → Extensions → Extension Developer → Install Extension → pick the .mcpb.
Enable the extension.
Tool | Annotation | What it does |
| read-only | All tmux sessions with name, windows, created/activity timestamps, attached flag |
| read-only | Exact-match check for a session name |
| read-only | Windows within a session (index, name, active, pane count) |
| read-only | Last N lines of the session's active pane (default 100, max 10000) |
| destructive | Start a detached session; optionally run an initial shell command |
| destructive | Send key combos or text to the active pane (Enter appended by default) |
| destructive | Terminate a session (sends SIGHUP to all processes inside) |
Start a training run:
"Start training run
b8-c1: activate myrdna4-trainvenv and run train.py."
new_session name=b8-c1 command="source ~/.venvs/rdna4-train/bin/activate && python /media/luke/Storage\ Device\ 1/NeuroForge/train.py b8-c1"
Check on it later:
"Is training
b8-c1still going? Show me the last 50 lines."
capture_pane name=b8-c1 lines=50
Interrupt a hung run:
"The training is stuck — send Ctrl+C."
send_keys name=b8-c1 keys="C-c" enter=false
Wrap up:
"Kill the session."
kill_session name=b8-c1
send_keys accepts either literal text (sent as keystrokes) or tmux key names. Common ones:
Keys | Effect |
| Ctrl+C (interrupt) |
| Ctrl+D (EOF / logout) |
| Escape key |
| Arrow keys |
| Enter (also appended automatically when |
| Space |
Pass enter: false when sending raw combos so you don't get an extra Enter after.
This extension runs entirely on your local machine and shells out only to the tmux binary. No data leaves your machine. No network I/O. No sockets. No files written outside of tmux's own per-user server socket (default /tmp/tmux-$UID/default).
The information visible to Claude includes session names, pane contents (the text you or your programs have printed), and session metadata (created/activity timestamps, window/pane counts). send_keys and kill_session can affect any process running inside a managed session, so treat it with the same trust level you'd give to a user typing into your terminal.
"tmux is not installed" — run sudo apt install tmux.
"can't find pane" errors — generally means the named session was killed mid-operation. Call has_session first, or use list_sessions to see what's actually running.
Session name restrictions — names cannot contain ., :, |, or whitespace. The . and : are tmux target separators; | is this server's field delimiter; whitespace is rejected on principle.
Session doesn't survive my initial command — by design, new_session always starts a shell; the command argument is sent as keystrokes into that shell. That's what keeps the session alive after the command finishes. If you passed command directly to tmux new-session it would exit when the command did.
Single ~300-line Node.js script, zero npm dependencies. Rebuild the .mcpb:
cd bundle-source
zip -j ../Sessions.mcpb manifest.json package.json server.js README.md LICENSE icon.png glama.jsonMIT. See LICENSE.
claude-terminal-mcp — shell, filesystem, and background jobs (for shorter-lived commands where tmux would be overkill).
claude-linux-mcp — X11 desktop control.
claude-rocm-mcp — AMD GPU monitoring; use alongside this one to check GPU health during training.
Capture the last N lines visible in the session's active pane (default 100, max 10000). Returns the joined text. The primary primitive for "is my training still running? show me the latest output".
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name. | |
| lines | No | Number of lines to capture (default 100). |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnly and non-destructive behavior. The description adds that it captures from the 'active pane' and returns 'joined text', which is useful behavioral context beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences: first technical with defaults/limits, second a relatable use case. No wasted words, information is front-loaded and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple read-only tool with two parameters and no output schema, the description covers purpose, behavior, parameters, and use case fully. No gaps.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Input schema has 100% coverage with descriptions for both parameters. The description adds the default value for 'lines' (100), which is not in the schema, giving minor additional value. Baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Capture the last N lines'), the resource ('session's active pane'), defaults and limits, and a concrete use case. It distinguishes from sibling tools which manage sessions or send keys, not capture output.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides a clear context for use ('is my training still running?') but does not explicitly state when not to use or name alternatives. However, the sibling tools imply that this is the sole tool for capturing output.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Check whether a named tmux session exists. Cheap precondition for capture_pane, send_keys, or kill_session.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name. Cannot contain ".", ":", "|", or whitespace. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint=true and destructiveHint=false. Description adds that the operation is 'cheap', which is valuable behavioral context beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, no wasted words, front-loaded with purpose. Efficient and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the simplicity of the tool (one parameter, no output schema), the description is complete: it explains purpose, usage context, and constraint hints.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with the parameter name described and constraints noted. Description does not add additional semantic meaning beyond what the schema provides, so baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Description clearly states the tool checks if a tmux session exists, using a specific verb and resource. It distinguishes itself from sibling tools by mentioning it's a precondition for three specific actions.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Description explicitly states it's a cheap precondition for capture_pane, send_keys, or kill_session, providing clear usage context. No exclusions or alternatives are mentioned, but the context is sufficient.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Terminate a named tmux session. Any processes running inside are sent SIGHUP by tmux. Errors if the session does not exist.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds beyond annotations: details SIGHUP behavior and error condition if session does not exist. Matches destructiveHint.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two concise sentences, front-loaded with primary purpose. No wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Complete for a simple kill tool with one parameter and no output schema. Covers purpose, behavior, and error case.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema has 100% coverage but only a minimal description for the 'name' parameter. No additional semantics added in tool description.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Terminate a named tmux session' with a specific verb-resource pair. Distinct from sibling tools like capture_pane or list_sessions.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Conveys when to use (to terminate a session) and mentions consequences (SIGHUP, error if missing). Could note alternatives but sufficient.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
List all tmux sessions on the current user's tmux server. Returns name, window count, created/activity timestamps (ISO 8601), and attached status. Returns an empty list when no tmux server is running.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint and destructiveHint. Description adds beyond that by detailing return fields (ISO 8601 timestamps, attached status) and the edge case of an empty list when no tmux server is running.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, front-loaded with the main action, and every word adds value. No fluff or redundancy.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given no parameters, no output schema, and annotations, the description fully covers what the tool does, its return values, and a key edge case (no server running).
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
No parameters exist, and schema coverage is 100% (trivially). Per guidelines for 0 parameters, baseline is 4. Description does not need to add parameter details.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Description clearly states 'List all tmux sessions' with specific return fields (name, window count, timestamps, attached status). It distinguishes from sibling tools like kill_session and new_session by focusing on listing only.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage for reading sessions, not modifying them. However, it does not explicitly state when not to use or mention alternatives. The context from sibling tools helps, but clarity could be improved.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
List windows within a named session (index, name, active flag, pane count).
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false, so the description adds the return fields (index, name, active flag, pane count). However, it does not disclose behavior if the session does not exist or any other edge cases. Adds some context but not rich behavioral details.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, concise sentence (12 words) with no wasted words. It is front-loaded with the action 'List windows' and immediately clarifies scope and return fields.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple read-only list tool with 1 parameter and no output schema, the description is fairly complete: it specifies what it does, what it returns, and the required input. It could mention that the session must exist, but that is implied. Sibling tools provide additional context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% (the only parameter 'name' is described as 'Session name'). The description reinforces that the session is named but adds no new semantic meaning beyond the schema. Baseline 3 for high coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'List' and the resource 'windows within a named session', and specifies return fields (index, name, active flag, pane count). This distinguishes it from sibling tools like list_sessions (list sessions) and capture_pane (capture pane output).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage when you have a session name and want to see its windows, but does not explicitly state when to use this tool versus alternatives like list_sessions or when not to use it. No guidance on prerequisites (e.g., session must exist).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Start a new detached tmux session. Always starts a shell (so the session survives after the initial command finishes). If command is given, it is sent to the shell as keystrokes + Enter, so aliases, venvs, and functions work as expected. Errors if the session name already exists.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name (unique). Cannot contain ".", ":", "|", or whitespace. | |
| command | No | Optional initial command to run inside the shell (e.g. "cd /path && python train.py"). | |
| cwd | No | Optional starting working directory for the session. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds significant behavioral details beyond annotations: detached, always starts shell, command sent as keystrokes enabling aliases, errors on duplicate name. No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences with no waste. First sentence states purpose, second explains key behavior, third clarifies command detail and error condition. Front-loaded and efficient.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Covers purpose, behavior, error conditions, and parameter semantics. No output schema needed. Complete for a creation tool with 3 parameters.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so baseline is 3. Description adds key nuance: command is sent as keystrokes + Enter, preserving aliases and venvs. This raises the score.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool starts a new detached tmux session, which is a specific verb + resource. It distinguishes from siblings like 'kill_session' by focusing on creation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Describes when to use (to start a session) and conditions: always starts a shell, errors if name exists. No explicit comparison to alternatives, but context is clear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Send key combos or text to the session's active pane. Use for interrupts (C-c), end-of-input (C-d), or typing a command. Text is sent literally. Enter is appended by default; set enter=false for raw key combos.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Session name. | |
| keys | Yes | Key combo (e.g. "C-c", "C-d", "Escape") or literal text to type. | |
| enter | No | Append an Enter keypress after the keys. Default true. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate destructive and open-world hints; the description adds detail: text is sent literally, Enter appended by default, and raw combos require enter=false. No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Three concise sentences, front-loaded with purpose, then specific guidelines. No wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Covers key behavioral aspects; lacks description of return values, but given no output schema and the nature of the action (send), this is acceptable. Sibling tools are listed for context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema covers 100% of parameters; description enriches meaning by explaining literal sending and enter default behavior, going beyond what the schema provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb (send), resource (key combos or text to session's active pane), and specific use cases (interrupts, end-of-input, typing a command). It distinguishes from sibling tools like capture_pane or kill_session.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides clear when-to-use guidance (interrupts, end-of-input, typing) and explains the enter parameter behavior. Does not explicitly mention when not to use or alternatives among siblings, but sibling tools are sufficiently different.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Each tool has a clearly distinct purpose: capturing output, checking existence, killing, listing sessions, listing windows, creating, and sending keys. No overlap in functionality.
All tools follow a verb_noun pattern with underscores. Minor deviations: 'has_session' uses 'has' as a verb and 'new_session' uses 'new' as verb, but overall pattern is consistent.
7 tools is well-scoped for managing tmux sessions. It covers essential operations without being excessive or insufficient.
Covers creation, listing, state checking, interaction (send/capture), and termination. Minor gaps like renaming sessions or creating windows, but adequate for its monitoring purpose.
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