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List Aircraft L-Vars

msfs_list_lvars
Read-onlyIdempotent

List every L-var currently registered by the loaded aircraft, with optional prefix filtering and pagination. Use when the aircraft has no bundled catalog or you need full coverage beyond catalog entries.

Instructions

Enumerate the L-vars registered by the currently loaded aircraft.

Asks the MobiFlight WASM module for its L-var list and collects the response. The module caps its reply at 1000 names but still reports the list as complete when it does -- see 'truncated' in the result, which is set whenever that cap was hit. A busy add-on setup (e.g. GSX) can crowd an aircraft's own L-vars out of a capped response entirely; msfs_get_lvar reads any name directly regardless of whether it showed up here.

Returns bare names only -- no description, category, or writability per variable, unlike msfs_search_lvars' catalogued rows. Use msfs_search_lvars / msfs_browse_lvar_catalog for aircraft with a bundled catalog when that detail is what you need; use this tool for aircraft that have none, or to see everything currently registered regardless of catalog coverage.

Internally sends a harmless no-op RPN command immediately before the WASM request, to re-arm the module against a quirk where it otherwise gives no response to a request byte-identical to the one it just answered (see _send_list_request's own docstring below for the full story). This creates no variable and has no effect on the aircraft, so calling this repeatedly is safe -- but the underlying quirk is a third-party module behavior this project does not control, so NO_LVARS_RETURNED below stays the honest report for the rare case where even the re-arm doesn't help, rather than this call ever assuming success. Requires the MobiFlight WASM extension.

A listing that stops without the module's end-of-list marker returns LVAR_LIST_INCOMPLETE rather than the names collected so far: an arbitrary prefix of the list is indistinguishable from a complete listing of that size once returned, so it is refused the same way msfs_get_nearby_airports refuses a timed-out facility collection.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
limitNoMaximum results
offsetNoResults to skip
filter_prefixNoOnly return names starting with this prefix, e.g. 'A32NX', 'WT_CJ4', 'XMLVAR'. Case-insensitive.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. First observedv1.0.1

TDQS

A4.6/5.0
Behavior5/5

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

Even with readOnlyHint, idempotentHint, and openWorldHint annotations, the description adds substantial behavioral context: the 1000-name cap and 'truncated' flag, the risk of add-on crowding, the internal no-op RPN re-arm quirk, and explicit failure modes like NO_LVARS_RETURNED and LVAR_LIST_INCOMPLETE. Nothing contradicts 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?

The description is long but front-loaded with the core purpose and packed with necessary caveats. Some internal-mechanism detail, such as the RPN re-arm story, could be tightened, but it earns its place by explaining a real behavioral quirk that could otherwise confuse an agent.

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?

The description covers prerequisites (MobiFlight WASM), result semantics (truncation, incomplete responses), failure modes, and sibling alternatives. Since an output schema exists, the lack of a full return-structure listing is not a gap; the description provides everything needed to invoke and interpret this tool correctly.

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

Parameters3/5

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

Schema description coverage is 100%, with limit, offset, and filter_prefix all documented in the input schema. The tool description does not add parameter-specific detail beyond the schema, so the baseline of 3 is appropriate; it neither improves nor harms parameter understanding.

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: 'Enumerate the L-vars registered by the currently loaded aircraft.' It clearly differentiates this from siblings like msfs_search_lvars and msfs_get_lvar by noting it returns bare names only and that msfs_get_lvar can read any name directly.

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?

The description gives explicit selection guidance: use msfs_search_lvars / msfs_browse_lvar_catalog when catalogued detail is needed, and use this tool for aircraft without a catalog or to see everything currently registered. It also notes when msfs_get_lvar is the better fallback, making the usage boundary unambiguous.

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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