figma_update_variable

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

With no annotations provided, the description carries the full burden and mostly succeeds: it discloses the Desktop Bridge plugin dependency, the mode/value coupling rule (value requires modeId), and that description maps to the DTCG $description field. It omits reversibility and whether unspecified mode values are left untouched, which would complete the mutation contract.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action, then constraints, alternative, prerequisite, and type formats in labeled chunks. Dense but every clause carries operational information; mild run-on density from stacked abbreviations keeps it from a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 4-parameter mutation with no annotations and no output schema, the description supplies prerequisites, format rules, plugin requirement, and the batch alternative. It could add what the tool returns or whether omitted fields are preserved, but nothing needed to call it correctly is missing.

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

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

Schema coverage is 100%, so formatting is already documented, but the description adds semantics the schema does not: the conditional dependency between modeId and value, the at-least-one-of requirement, and a compact per-type value cheat sheet (COLOR/FLOAT/STRING/BOOLEAN) that lets an agent construct the call without cross-referencing the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence states a specific verb and resource ("Update a single variable's value and/or its description") and immediately delineates the two editable aspects. It separates itself from the batch sibling by describing itself as single-variable and pointing to figma_batch_update_variables for bulk work.

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

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

It names the alternative explicitly with a quantified tradeoff ("10-50x faster") and gives the prerequisite that IDs come from figma_get_variables first. The "At least one of {modeId+value} or {description} is required" line defines the valid invocation envelope.

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