display_message

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

Annotations already declare non-read-only, idempotent and non-destructive, and the description adds real behavioral context beyond them: it destroys/replaces current content, rejects oversized text instead of clipping, and defines the auto-clear window. Return value and failure behavior for oversized text are not described.

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?

Four short sentences, front-loaded with the core action, and each sentence conveys a distinct operational fact. "Short messages work best on 3.5 inches" is the weakest line because it doesn't quantify the limit it implies.

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 mutating display tool with no output schema, the description covers replacement behavior, sizing limits, and persistence semantics. What remains unclear is the theme options and how oversized rejection is surfaced to the caller.

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 0%, so the description must carry parameter meaning; it fully explains duration_seconds but says nothing about theme (three enum values) or title. Roughly half the parameters remain undocumented.

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?

States a specific verb and resource ("Show readable text on the Pi screen"), which clearly separates it from image-oriented siblings like display_image and clear_display. It never names a sibling explicitly, so differentiation is implicit rather than spelled out.

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 duration semantics (0 = persistent, 1–86400 = auto-clear) and the size constraint imply usage, but there is no explicit when-to-use / when-not guidance versus clear_display, preview_display, or speak. An agent can infer intent but must guess at edge cases.

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