Set the characters of a text layer

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

Annotations already indicate this is a destructive write operation. The description adds meaningful non-obvious behavior: the font is loaded first, and missing fonts cause a refusal rather than silent substitution. This gives the agent important expectations about failure modes beyond what annotations provide.

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?

Two sentences with no filler. The first sentence states the core purpose, and the second adds the critical font-loading behavior. Every sentence earns its place.

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 two-parameter mutation tool with rich annotations and full schema coverage, the description adequately covers the operation and a key edge case. It does not describe return values or explicit error behavior beyond missing fonts, but those are not essential for correct invocation of this simple tool.

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 description coverage is 100%, so the input schema already documents both nodeId and text clearly. The description adds no additional parameter-specific meaning beyond restating that text is 'new characters' and nodeId is the 'TEXT node to retype,' which is already covered by 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 description states a specific verb ('Replaces'), a specific resource ('the text of one TEXT node'), and clearly distinguishes this from sibling text-related tools like figma_create_text or figma_set_text_style. It is immediately obvious what the tool does.

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?

The intended use is implied: use this tool to change the text content of an existing text layer. However, there is no explicit guidance on when to prefer this over alternatives such as figma_create_text or figma_set_text_style, and no mention of constraints like requiring a selected node or a text layer.

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