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

With readOnlyHint=true already covering safety, the description adds real behavioral context: it returns both native markdown-ish syntax and Unicode mathematical letters, warns that Unicode variants are not searchable and are problematic for screen readers, and notes there is no cost or allowance consumed. It does not describe the exact response payload, which keeps it from a 5.

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?

Three sentences, each load-bearing: the capability, the dual output format with usage preference, and the cost note. The most decision-relevant fact (what it returns) is front-loaded.

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?

No output schema exists, so the description must carry the return-value burden; it explains the two output formats conceptually but not the response structure (field names/shape). Given the low complexity and only two required params, this is nearly complete.

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 both parameters and the enum values are already documented in the schema. The description reinforces style behavior (which styles lack native syntax or Unicode digits) but adds little tool-call syntax beyond the schema's baseline.

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 ('Produce bold or italic text for YouTube') and immediately contrasts itself with tools like runsheet_count_characters or runsheet_preserve_line_breaks by being the styling transform. An agent can identify the function without opening the schema.

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?

Gives clear conditional guidance on output choice: prefer native syntax where it works, Unicode only where syntax renders literally (titles/descriptions). It does not name an alternative styling sibling (there is none) or state exclusions for when not to call it, so it falls short of a 5.

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