PostFader V10 — FL Studio MCP Server

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fl_set_track_eq

Destructive

Set gain or frequency on one band of a track's built-in three-band EQ in FL Studio. Optionally verify the band's prior state before writing to prevent overwriting edits.

Instructions

Set gain and/or frequency on one built-in EQ band; at least one is required.

Input Schema

TableJSON Schema

Name	Required	Description
`band_index`	Yes	Which band of the track's built-in three-band EQ: 0 low, 1 mid, 2 high.
`track_index`	Yes	Zero-based mixer index. Index 0 is Master and is refused unless allow_master is true.
`allow_master`	No	Deliberately target the master bus at index 0.
`expected_before`	No	Optional expected gain and/or frequency; refuse if any supplied field changed.
`gain_normalized`	No	Band gain, normalized 0.0 to 1.0; 0.5 is flat. Omit to leave the gain alone.
`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.
`frequency_normalized`	No	Band centre frequency, normalized 0.0 to 1.0. Omit to leave the frequency alone.

Output Schema

TableJSON Schema

Name	Required	Default
`after`	Yes
`before`	Yes
`verified`	Yes
`warnings`	No
`applied_at`	Yes
`band_index`	Yes
`track_index`	Yes
`gain_verified`	No
`project_saved`	No
`bridge_command`	No	mixer.set_eq
`schema_version`	No	1.0
`targeted_master`	No
`frequency_verified`	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
`requested_gain_normalized`	No
`session_precondition_applied`	No
`requested_frequency_normalized`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv10.0.0Sep 14, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the write nature and side-effect risk are known. The description adds the at-least-one constraint but no additional behavioral context such as immediate application, undo behavior, or refusal conditions. With annotations covering the safety profile, this is adequate but not enriched.

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?

One compact sentence with the action front-loaded and the critical at-least-one condition included. No filler or redundant restatement of schema fields.

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?

The rich schema descriptions, output schema, and annotations cover parameter semantics, return values, and side-effect risk. The description supplies the one missing invocation rule (at least one of gain/frequency) and enough resource scoping to make a correct call. It does not over-explain details already present in structured data.

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 description coverage is 100%, so the baseline is 3. The description adds a valuable cross-parameter constraint ('at least one is required') that the JSON schema does not enforce, and maps 'gain and/or frequency' to the two optional parameters. This goes beyond what the schema states.

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 uses a specific verb ('Set'), names the exact resource ('one built-in EQ band'), and states what can be changed ('gain and/or frequency'). It clearly distinguishes this from plugin-param and other mixer setters by limiting scope to the built-in EQ, and it includes the at-least-one requirement.

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 'built-in EQ band' qualifier gives context and implies this is not for plugin EQs, but there is no explicit when-to-use or alternative routing (e.g., 'use fl_set_plugin_param for plugin EQs'). The usage is inferable but not spelled out.

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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