capcut-mcp

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capcut_add_audio

Add music or voice-over to a CapCut draft audio track with volume, fade in/out, and timing; dry-run by default before writing to disk.

Instructions

Add music or a voice-over (audio file) on an audio track, with volume and optional fade in/out. Default track "music". Dry-run by default.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "draft": "<draft>",
      "path": "<path>"
    },
    "name": "capcut_add_audio"
  }
}

Input Schema

Name	Required	Description	Default
`in_s`	No	Trim start inside the source.
`path`	Yes	Absolute path of the media file.
`draft`	Yes	Draft folder name inside the drafts root (from capcut_list_drafts).
`track`	No		music
`volume`	No	1 = original level. Background music: 0.2-0.4.
`dry_run`	No	true (default): return the plan only. false: write to disk (CapCut must be closed).
`start_s`	No	Timeline position.
`fade_in_s`	No
`duration_s`	No	Length on the timeline (default: rest of the file after in_s; read from MP4/MOV/M4A/WAV).
`fade_out_s`	No
`media_duration_s`	No	Full source length, if the file length cannot be read (MP3, MKV...).

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.0Oct 15, 2026

TDQS

B3.4/5.0

Behavior3/5

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

With no annotations, the description carries the full burden. It does disclose two key behavioral traits: the dry-run default (so nothing is written unless overridden) and the default 'music' track. It omits the requirement that CapCut be closed and says nothing about permissions or reversibility, so it is helpful but incomplete for a write-capable tool.

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?

Three short clauses, front-loaded with the action and followed by capability and default notes. No wasted words, though it is a bit terse for an 11-parameter tool.

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

Completeness3/5

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

For an 11-parameter, unannotated tool with no output schema, the description is only minimally sufficient. It covers the core action and dry-run default but leaves sibling relationships and operational prerequisites (e.g., draft must exist, CapCut closed) to the schema or inference.

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

Parameters3/5

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

Schema description coverage is 73%, so the schema already documents most parameters (volume scale, dry_run semantics, duration fallbacks). The description adds only the notion of volume and fade in/out, largely restating what the schema provides, so baseline 3 applies.

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 music or a voice-over (audio file) on an audio track') plus capabilities (volume, fade in/out). An agent can tell this adds audio content. It does not, however, explicitly distinguish itself from siblings like capcut_add_clip or capcut_duck_music, which also touch the audio timeline.

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?

The description implies when to use it (music/voice-over placement) and notes the default track is 'music'. But it gives no when-not guidance and does not route the agent to alternatives such as capcut_duck_music for background-music ducking or capcut_add_clip for generic media.

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