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

Beyond the annotations (readOnly, idempotent, closed-world), it discloses real behavioral traits: lookalike characters rather than real fonts, digits/accented letters staying plain, degraded screen-reader output, no storage or logging of phone numbers/text, and no account access or message sending. It also prescribes how to render the result, which is exactly the context an agent needs.

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?

The description front-loads the core action and the style list, then layers caveats and the display instruction. It is dense but each sentence carries information; the privacy sentence is slightly boilerplate but still relevant to user trust.

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?

An output schema exists and the description still tells the agent to render structuredContent.styledText verbatim in a fenced code block, closing the loop on return-value handling. The only meaningful omission is any explanation of the locale parameter.

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 67%; text and style are documented in the schema, but locale has no description in either the schema or the description, so its purpose is left unspecified. The style list is repeated from the enum rather than adding new meaning, so the description adds little beyond 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 and resource ('Rewrite the user's text in one decorative Unicode style') and enumerates the eight styles, so the agent knows exactly what the tool produces. It does not, however, distinguish itself from the sibling format_whatsapp_text, which sounds closely related.

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?

'Call it once the user has picked a style from this list' gives a clear triggering condition and sequencing rule. It still leaves the agent guessing when to choose this over format_whatsapp_text, so it falls short of explicit alternative routing.

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