PostFader V10 — FL Studio MCP Server

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fl_set_mixer_send

Destructive

Create or remove a mixer send route between two tracks. Set whether the route exists, then adjust its level separately; optionally verify current state before changing.

Instructions

Route one mixer track to another, or stop routing it there.

A stated state, never a toggle. Sending *to* Master needs no flag; only
sending *from* Master does. Set the amount with `fl_set_mixer_send_level`
afterwards -- this call only decides whether the route exists.

Input Schema

TableJSON Schema

Name	Required	Description
`enabled`	Yes	True to create the send, False to tear it down.
`track_index`	Yes	Zero-based index of the sending track.
`allow_master`	No	Required only to send FROM track 0.
`expected_before`	No	Optional expected current route state; refuse if it changed.
`session_fingerprint`	No	Optional bridge/project-session fingerprint from a recent read. The write refuses after bridge reload or a reported project load. This is a concurrency guard, not authentication or a durable project identity.
`destination_track_index`	Yes	Zero-based index of the receiving track.

Output Schema

TableJSON Schema

Name	Required	Default
`verified`	Yes
`warnings`	No
`applied_at`	Yes
`track_index`	Yes
`after_enabled`	No
`project_saved`	No
`before_enabled`	No
`bridge_command`	No	mixer.set_send
`schema_version`	No	1.0
`targeted_master`	No
`level_normalized`	No
`requested_enabled`	Yes
`undo_point_created`	No
`verification_basis`	No	readback_on_a_later_fl_idle_tick
`session_fingerprint`	No
`verification_summary`	Yes
`destination_track_index`	Yes
`expected_before_applied`	No
`session_precondition_applied`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv10.0.0Sep 14, 2026

TDQS

A4.7/5.0

Behavior4/5

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

Annotations already flag mutation and destructiveness; the description adds genuinely non-obvious runtime behavior: it is 'a stated state, never a toggle,' has an asymmetric Master-flag requirement, and scopes effects to route existence only. It doesn't add caveats about expected_before/session_fingerprint, but the schema covers those, so the added behavior context goes beyond annotations without contradiction.

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?

Four short sentences front-load the core action and then add only the behavioral details an agent needs; every sentence earns its place, and the call-to-sibling for level setting is appended without bloat.

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?

Combined with a rich schema that documents all six parameters and a clear output schema, the description supplies the missing operating semantics: route existence vs. level, absolute state, and the Master exception. No decision-relevant gap remains for selecting or calling the tool correctly.

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 already 100%, so the baseline is a 3, but the description adds semantic value for the boolean parameter: 'A stated state, never a toggle' tells the agent that enabled is absolute, not a flip. It also clarifies allow_master's asymmetry ('Sending to Master needs no flag; only sending from Master does'), complementing the schema's terse 'Required only to send FROM track 0.'

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 opening sentence names both actions ('Route one mixer track to another, or stop routing it there') with a specific verb and resource, making the tool's function immediately clear. It also distinguishes this from level-setting via a terse but precise scoping statement, so an agent won't confuse it with sibling mixer tools.

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 directs the agent to use fl_set_mixer_send_level for the amount and clarifies that this call 'only decides whether the route exists,' which defines the boundary between the two tools. The master-flag guidance ('only sending from Master does') is a concrete when-to-include-flag rule.

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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