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reaper-mcp

by TwelveTake-Studios
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add_envelope_point

Add a point to an envelope. A missing Volume, Pan, Width, Mute or Trim Volume envelope (or a Pre-FX one) is created first: REAPER starts it with a point at 0:00 holding the track's current value, and the response has envelope_created.

Instructions

Add a point to an envelope. A missing Volume, Pan, Width, Mute or Trim Volume envelope (or a Pre-FX one) is created first: REAPER starts it with a point at 0:00 holding the track's current value, and the response has envelope_created.

Args: envelope_name: Envelope name. time: Time position in seconds. value: Raw value. Pan -1..1 with +1 = LEFT (the reverse of set_track_pan); Width -1..1; Mute 0 = muted, 1 = unmuted. A raw volume value depends on the envelope's scaling, so use value_db there. shape: Point shape (0=linear, 1=square, 2=slow start/end, 3=fast start, 4=fast end, 5=bezier). value_db: Level in dB for Volume, Volume (Pre-FX) and Trim Volume; -150 is silence. Pass this or value.

Returns: point_index, value, and shown: the value as REAPER displays it ("-6.00dB", "50%L").

Input Schema

NameRequiredDescriptionDefault
timeYes
shapeNo
valueNo
value_dbNo
track_indexYes
envelope_nameYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv1.9.3
    • addedInput schema / properties / value / anyOf
      Added value: +[
+  {
+    "type": "number"
+  },
+  {
+    "type": "null"
+  }
+]
    • addedInput schema / properties / value / default
      Added value: +null
    • removedInput schema / properties / value / type
      Removed value: -"number"
    • addedInput schema / properties / value_db
      Added value: +{
+  "anyOf": [
+    {
+      "type": "number"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null
+}
    • changedInput schema / required
      Previous value: -[
-  "track_index",
-  "envelope_name",
-  "time",
-  "value"
-]New value: +[
+  "track_index",
+  "envelope_name",
+  "time"
+]
  2. First observedv1.7.3

TDQS

A3.8/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only supply destructiveHint=false, and the description adds real behavioral context: a missing envelope is created with a point at 0:00 holding the track's current value, and the response carries envelope_created. It also explains the mutation's side effect and the return payload (point_index, value, shown) despite no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the action and the auto-create behavior, then a structured Args/Returns block. Slightly verbose with awkward line-wrapping in Args, but no sentence is filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With 6 parameters, an output payload and no output schema, the definition covers behavior, units, and return shape well enough to call it correctly. Gaps remain on valid envelope_name values and what track_index refers to, which matter for a 3-required-param call.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, so the description must carry the load, and it largely does: value ranges and polarity for Pan (+1 = LEFT, explicitly the reverse of set_track_pan), Width, Mute, all five shape enum codes, and value_db with -150 as silence. Only track_index and the valid envelope_name strings go undocumented.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("Add a point to an envelope") and immediately scopes it to track envelopes by naming Volume, Pan, Width, Mute and Trim Volume. It does not explicitly name the sibling add_fx_envelope_point, so an agent must infer the boundary from the field list rather than from a sentence.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Useful in-band guidance is present: which fields get auto-created, and the rule "Pass this or value" for the value/value_db pair. But there is no explicit when-not or alternative routing (e.g. use add_fx_envelope_point for FX parameters instead), so usage context is implied rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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