PostFader V10 — FL Studio MCP Server

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fl_set_mixer_color

Destructive

Set a mixer track's color in FL Studio using a 0xAABBGGRR integer; accepts FL's high-byte differences and supports optional concurrency protection.

Instructions

Set a mixer color, accepting FL-owned differences in the high byte.

Input Schema

TableJSON Schema

Name	Required	Description
`color`	Yes	FL color word as unsigned 0xAABBGGRR integer.
`track_index`	Yes	Zero-based mixer index. Index 0 is Master.
`allow_master`	No	Required to target mixer track 0.
`expected_before`	No	Optional expected current FL color word.
`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.

Output Schema

TableJSON Schema

Name	Required	Default
`verified`	Yes
`warnings`	No
`applied_at`	Yes
`after_color`	No
`track_index`	Yes
`before_color`	No
`project_saved`	No
`bridge_command`	No	mixer.set_color
`schema_version`	No	1.0
`requested_color`	Yes
`targeted_master`	No
`undo_point_created`	No
`verification_basis`	No	readback_on_a_later_fl_idle_tick
`session_fingerprint`	No
`verification_summary`	Yes
`expected_before_applied`	No
`session_precondition_applied`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv10.0.0Sep 14, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already communicate that this is a destructive, non-idempotent write operation, so the description's job is lighter. It adds a useful behavioral detail: the tool tolerates FL-owned differences in the high byte of the color word. This is non-obvious and valuable for correct use.

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 a single, front-loaded sentence with no filler. Every word contributes meaning, and the key behavior is stated immediately.

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?

Given the rich input schema, output schema, and annotations, the short description is mostly sufficient. The main missing piece is explicit when/why to choose this tool over sibling mixer setters, but the schema compensates for most operational details.

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?

The input schema already documents all five parameters with 100% coverage, so the baseline is 3. The description adds extra semantic meaning beyond the schema by clarifying that the high byte of the color value may differ from what FL reports, helping agents understand how strict the color value needs to be.

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 states a specific verb and resource ('Set a mixer color') and adds a meaningful nuance about accepting FL-owned high-byte differences. It clearly distinguishes this tool from sibling mixer setters (volume, pan, mute, etc.) without needing to inspect the schema.

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

Usage Guidelines2/5

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

No explicit guidance is given about when to use this tool versus alternatives, and no prerequisites or exclusions are mentioned. The intended use is only implied by the name and description, which is insufficient given the large family of mixer-related setter tools.

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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