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Python
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set_arrangement_time

Idempotent

Move the Arrangement playhead to any beat and read back the verified position, setting the playback start point without starting transport.

Instructions

Move the Arrangement playhead to a beat and read the position back.

Writes ``song.current_song_time``. This moves where playback would start. It
does not start it. Use play to begin, or play with ``from_beat`` to do both in
one call.

Returns:
    Dictionary with the write confirmation and the read-back song time.

Note:
    Writing ``song.current_song_time`` is bounded by ``song.song_length``;
    attempting to set a position past ``song_length`` fails with Live error
    ``"Cannot set the Songtime behind the Songlength"``. Transport playback
    in Session view advances freely past ``song_length``.

    Do not sample a moving transport through lom_batch. A read that follows a
    jump inside the same batch still reports the position from before the move,
    and it reports it without an error (see lom_batch). One call per position.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
at_beatYesPosition on the Arrangement timeline in beats from the start, where beat 0 is the beginning of the song. Fractional beats are accepted, so 33.5 is the second half of bar 9 in 4/4.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.1.1
    • addedInput schema / properties / at_beat / description
      Added value: +"Position on the Arrangement timeline in beats from the start, where beat 0 is the beginning of the song. Fractional beats are accepted, so 33.5 is the second half of bar 9 in 4/4."
  2. First observedv0.1.0

TDQS

A4.7/5.0
Behavior5/5

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

The description discloses behaviors well beyond the annotations: it states it writes song.current_song_time, that writes are bounded by song_length, the exact Live error on failure, and the stale-read behavior inside lom_batch. This gives the agent important execution expectations that annotations alone do not convey.

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

Conciseness5/5

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

The description is well structured: a front-loaded one-sentence summary, then an expandable note and return statement. The warnings about song_length and lom_batch are necessary behavioral context, not filler, and every sentence earns its place.

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

Completeness5/5

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

For a single-parameter write-and-read tool, the description covers the primary action, the boundary condition, the failure mode, the batching caveat, and the relationship to playback tools. An agent has enough information to invoke it correctly and anticipate outcomes.

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 100%, and the schema already defines at_beat including beat origin and fractional beat acceptance. The tool description adds little parameter-specific meaning beyond the schema, so the baseline of 3 is appropriate.

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

Purpose5/5

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

The description opens with a specific verb and resource: 'Move the Arrangement playhead to a beat and read the position back.' It clearly identifies the operation and distinguishes it from starting playback, explicitly noting that play or play with from_beat handles playback.

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

Usage Guidelines5/5

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

The description gives explicit guidance on when to use this tool versus alternatives: 'Use play to begin, or play with from_beat to do both in one call.' It also warns against using lom_batch for sampling a moving transport and prescribes 'One call per position', which is actionable usage advice.

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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