Controls REAPER playback: play, stop, pause, record, toggle repeat, jump to start, or move the edit cursor to a beat position or marker/region.
Playback control. action: play, stop, pause, record, toggle_repeat, goto_start, goto (edit cursor to position_beats, or to a marker/region by number or name; moves playback too when playing). Returns play_state, position_sec and position_beats.
| Name | Required | Description | Default |
|---|---|---|---|
| action | Yes | ||
| marker | No | ||
| position_beats | No |
Changes observed during successful MCP inspections.
v0.6.0Input schema / properties / action / enumPrevious value: -[
- "play",
- "stop",
- "pause",
- "record",
- "toggle_repeat",
- "goto_start"
-]New value: +[
+ "play",
+ "stop",
+ "pause",
+ "record",
+ "toggle_repeat",
+ "goto_start",
+ "goto"
+]Input schema / properties / markerAdded value: +{
+ "type": [
+ "string",
+ "integer"
+ ]
+}Input schema / properties / position_beatsAdded value: +{
+ "minimum": 0,
+ "type": "number"
+}v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden; it does disclose an important side effect (goto moves playback when playing) and names the returned fields. However, it omits whether stop/record reset position or arm tracks, permission or project-state prerequisites, and error behavior for invalid markers.
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?
Front-loaded with purpose, then compact action semantics in a single pass with no filler. The deeply nested parenthetical makes the goto rules dense but every clause carries information.
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 3-parameter, no-annotation, no-output-schema tool it covers the return shape and the trickiest parameter interaction, which is good. Gaps remain around action/parameter pairing, precedence when both targeting params are given, and failure modes, so it is adequate rather than complete.
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 0%, so the description must compensate; it does explain goto's two targeting modes (position_beats vs marker by number or name), which is the most confusing part. It still doesn't state that marker and position_beats are only meaningful for goto, what happens if both are supplied, or that position_beats is non-negative.
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 opens with a clear domain statement ("Playback control") and then enumerates the exact actions available, so an agent knows this drives play/stop/pause/record and cursor navigation. It clearly is not the same as siblings like status, action, or render, though it never names those siblings to reinforce the distinction.
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?
There is no explicit statement of when to use this tool versus adjacent tools (status vs action vs transport), and no conditions or exclusions. The action list implies usage, but the only real guidance is about goto's targeting options, not about tool selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.