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mpfb_list_expressions

Read-onlyIdempotent

List saved MPFB expressions with their fragment identifiers and face units, showing which files are readable or shadowed so you can choose valid inputs.

Instructions

List the saved expressions MPFB can apply - named, weighted combinations of ARKit face units such as a smile - as mpfb_apply_expressions takes them. Changes nothing.

result's expressions is one entry each: fragment, the identifier to pass (library-relative, portable across machines), path (the absolute file, for checking), root, label, description, tags, author, license and face_units (what the expression sets). Not capped or paged.

roots lists the directories scanned, in MPFB's priority order, whether or not anything was found. unreadable names files MPFB skips because they do not parse. shadowed names files hidden behind a same-named file in a higher-priority root: MPFB cannot apply them.

faceunits01_installed is always present: without that asset pack no expression can be applied. refresh (default false) re-probes for the pack; the file scan itself is never cached.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`refresh`	No

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 3, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already cover readOnly/idempotent/destructive/openWorld, but the description adds substantial context beyond them: the file scan is never cached, refresh only re-probes the asset pack, unreadable files are skipped for parse failures, and shadowed files cannot be applied. These are real behavioral traits not derivable from the annotations.

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?

Front-loads purpose and the sibling relationship in the first sentence, then organizes output/roots/constraint details in labeled paragraphs. It is longer than strictly needed given an output schema exists (field-by-field enumeration is partly redundant), but each block adds semantics and nothing is wasted.

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?

Given a one-param list tool with an output schema, the description covers purpose, the routing to apply_expressions, output field semantics, directory scanning order, skip/shadow behavior, and the mandatory faceunits01 constraint. Nothing an agent needs to call or interpret it is missing.

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 0% for the single 'refresh' parameter, so the description must compensate, and it does: it explains refresh re-probes for the faceunits01 asset pack while the file scan is never cached. That meaningfully extends the bare boolean/default in the schema.

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?

States a specific verb (List) and resource (saved expressions), defines what an expression actually is (named, weighted combinations of ARKit face units), and explicitly ties it to the sibling mpfb_apply_expressions as the consumer. An agent can distinguish this from mpfb_get_expression and mpfb_apply_expressions immediately.

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

Usage Guidelines4/5

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

The description routes the agent clearly: this is the lookup that produces the 'fragment' identifier mpfb_apply_expressions takes, and 'Changes nothing' signals a safe read. It stops short of an explicit when-to-use/when-not statement or naming alternative list tools, so 4 rather than 5.

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