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als_write

Destructive

Edit a saved Ableton Live project file on disk. Wire sidechain compression, configure plug-in parameter strips, set XML attributes, or restore backups—with confirmation and verification before changes are applied.

Instructions

Edit a saved .als project file on disk. Requires confirm=True.

The target file must not be the one Live currently holds: Live writes its own memory
over the file when it next saves, without a conflict warning, and the edit is gone. Live
running on a different set is fine.

Returns:
    Dictionary reporting write status, changes made, and verification report.

Note:
    ``sidechain`` and ``configure`` reach what the LOM cannot; for the set open in Live
    use ``lom_set``, ``set_parameter`` or ``set_mix`` instead. Measured across the
    174-project corpus (docs/limits.md section 9), 74 of 82 projects in the house/trance
    BPM window use sidechain compression, median 6 wirings each.

    ``configure`` fills a plug-in's parameter strip whatever the strip currently holds.
    Two parameters written into an instance whose strip held nothing came back on reopen
    with their real values, writable through ``lom_set`` with ``read_back: applied``.
    Live allocates 128 slots per instance and leaves them all in the file, so nothing is
    inserted: three fields of an existing element are filled.

    ``attribute`` sets one attribute anywhere in the file, addressed by an ElementTree
    expression. An expression matching more than one element is refused unless ``index``
    picks one, and ``index`` counts the matches of that expression rather than tracks in
    the project: ``.//MidiTrack/Name/EffectiveName`` does not see the audio tracks at
    all. ``als_read`` with ``locate='tempo'`` or ``locate='track_names'`` answers with
    the expression, attribute and index for those fields; otherwise the expression is
    built by hand, and ``confirm=False`` resolves it against the file and reports what
    it selects.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`tap`	No	Where the sidechain listens on the source track: 'pre' before that track's own effects and fader, 'post' after them. Used by 'sidechain' only.	post
`path`	Yes	Filesystem path to the .als project to edit. A backup is written first and can be put back with the restore operation.
`index`	No	Which match to edit when the expression selects more than one element, counted from 0. An ambiguous expression is refused rather than resolved to the first match, so this is how to disambiguate.
`value`	No	For 'attribute', the new attribute value. For 'configure', the parameter strip assignment as '<index>=<name>; ...'.
`backup`	No	Path to the backup file to put back. Required by the 'restore' operation and read by no other.
`create`	No	True adds the attribute when the element does not already carry it. False refuses, which catches a misspelled attribute name instead of inventing a field Live will ignore.
`device`	No	Device index within the target track chain, counted from 0. Used by 'sidechain' and 'configure'.
`confirm`	No	True carries the edit out. False changes nothing and reports what the call requires, which is how to check the arguments first.
`attribute`	No	Which attribute of the selected element to set. Live stores most numbers under 'Value'. Used by 'attribute' only.	Value
`operation`	Yes	What to do. 'sidechain' wires a compressor to a trigger track, 'configure' fills a plug-in parameter strip, 'attribute' sets one XML attribute anywhere in the file, 'restore' puts a backup back. Each one reads a different subset of the arguments below.
`expression`	No	ElementTree path selecting the element to edit, e.g. './/MasterTrack/DeviceChain/Mixer/Tempo/Manual'. Used by 'attribute' only. Read the tree with als_read first.
`source_track`	No	Name of the track the compressor should listen to, which is usually the kick. Used by 'sidechain' only.
`target_track`	No	Name of the track carrying the device to edit, as it appears in Live. Used by 'sidechain' and 'configure'.
`allow_live_running`	No	True permits the edit while Live is running at all. The check behind it looks for a running Live process and cannot tell which set that process holds, so it is not a guard against editing the open one: only you know that. What matters is the file, not the process. Live open on a different set is harmless. Live holding this file overwrites the edit from memory when it next saves.

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed16 schema fields changedv0.1.1Sep 7, 2026

addedInput schema / properties / allow_live_running / description

Added value: +"True permits the edit while Live is running at all. The check behind it looks for a running Live process and cannot tell which set that process holds, so it is not a guard against editing the open one: only you know that. What matters is the file, not the process. Live open on a different set is harmless. Live holding this file overwrites the edit from memory when it next saves."

addedInput schema / properties / attribute / description

Added value: +"Which attribute of the selected element to set. Live stores most numbers under 'Value'. Used by 'attribute' only."

addedInput schema / properties / backup / description

Added value: +"Path to the backup file to put back. Required by the 'restore' operation and read by no other."

addedInput schema / properties / confirm / description

Added value: +"True carries the edit out. False changes nothing and reports what the call requires, which is how to check the arguments first."

addedInput schema / properties / create / description

Added value: +"True adds the attribute when the element does not already carry it. False refuses, which catches a misspelled attribute name instead of inventing a field Live will ignore."

addedInput schema / properties / device / description

Added value: +"Device index within the target track chain, counted from 0. Used by 'sidechain' and 'configure'."

addedInput schema / properties / expression / description

Added value: +"ElementTree path selecting the element to edit, e.g. './/MasterTrack/DeviceChain/Mixer/Tempo/Manual'. Used by 'attribute' only. Read the tree with als_read first."

addedInput schema / properties / index / description

Added value: +"Which match to edit when the expression selects more than one element, counted from 0. An ambiguous expression is refused rather than resolved to the first match, so this is how to disambiguate."

addedInput schema / properties / operation / description

Added value: +"What to do. 'sidechain' wires a compressor to a trigger track, 'configure' fills a plug-in parameter strip, 'attribute' sets one XML attribute anywhere in the file, 'restore' puts a backup back. Each one reads a different subset of the arguments below."

addedInput schema / properties / operation / enum

Added value: +[
+  "sidechain",
+  "configure",
+  "attribute",
+  "restore"
+]

addedInput schema / properties / path / description

Added value: +"Filesystem path to the .als project to edit. A backup is written first and can be put back with the restore operation."

addedInput schema / properties / source_track / description

Added value: +"Name of the track the compressor should listen to, which is usually the kick. Used by 'sidechain' only."

addedInput schema / properties / tap / description

Added value: +"Where the sidechain listens on the source track: 'pre' before that track's own effects and fader, 'post' after them. Used by 'sidechain' only."

addedInput schema / properties / tap / enum
```
Added value: +[
+  "pre",
+  "post"
+]
```

addedInput schema / properties / target_track / description

Added value: +"Name of the track carrying the device to edit, as it appears in Live. Used by 'sidechain' and 'configure'."

addedInput schema / properties / value / description

Added value: +"For 'attribute', the new attribute value. For 'configure', the parameter strip assignment as '<index>=<name>; ...'."

First observedv0.1.0Sep 5, 2026

TDQS

A4.9/5.0

Behavior5/5

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

The description goes well beyond the destructiveHint annotation by disclosing the backup-and-restore behavior, the confirm=False dry-run mechanism, the risk of Live overwriting edits, and detailed operational side effects such as fill-in-place behavior for configure and expression-match refusal for attribute. This is substantial behavioral context that an agent would otherwise have no way to infer.

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?

The description is long but well structured, with the core statement and safety requirement front-loaded, followed by returns and operation-specific notes. Most content earns its place due to the tool's complexity, though the corpus statistics about sidechain usage are arguably secondary and could be trimmed without losing essential guidance.

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 14-parameter, four-operation mutation tool with no openWorldHint and a destructive annotation, the description covers the critical context: when to edit, what gets changed, how to verify, how to avoid data loss, and how each parameter interacts with each operation. Combined with the rich schema and an output schema, nothing essential is left unexplained.

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

Parameters5/5

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

Although the schema coverage is 100%, the description adds significant meaning beyond the field definitions: it maps each operation to its relevant argument subset, explains confirm=True/False as a check-and-apply flow, and clarifies subtle semantics like index counting expression matches rather than project tracks. This materially helps an agent choose and populate parameters correctly.

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—'Edit a saved .als project file on disk'—and clarifies the scope by naming the sibling tools it is not, such as lom_set, set_parameter, and set_mix. It also distinguishes operations within the tool (sidechain, configure, attribute, restore), making its purpose immediately intelligible.

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?

It explicitly states when not to use the tool: the target file must not be the one Live currently holds, and warns about Live overwriting edits. It names the alternative tools to use for the set open in Live and references als_read for building expressions, giving an agent clear routing guidance without ambiguity.

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