ass_font_coverage

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

With no annotations, the description carries the full burden and does well: it discloses fontconfig-based resolution, that a substituted request is reported honestly, and that missing characters return codepoints plus covering fallback families. It does not state permissions or that the operation is read-only, but the read-only nature is strongly implied by 'check'.

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 operation is front-loaded in the first sentence, which is good. However, the long backtick-quoted enumeration of every return field is redundant given that an output schema already exists, making the passage longer than it needs to be.

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?

Return values are covered by the output schema, so that enumeration is surplus. Behavior and the family parameter are reasonably complete, but the missing bold/italic semantics and the absence of any sibling routing leave an agent guessing in a crowded font-related tool family.

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 0%, so the description must compensate. It does explain family resolution and the default-sans behavior when omitted (default_used), but it never explains the bold or italic flags or the required text parameter, leaving half the parameters undocumented in both places.

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 names a specific verb (checking coverage) and resource (characters of text against a font family), so an agent can grasp the operation immediately. It does not, however, differentiate itself from close siblings like ass_fonts_with_char, ass_glyph_check, or ass_match_font, so the boundary is left to inference.

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?

There is no when-to-use guidance, no mention of alternatives, and no task context (e.g. pre-flight check before rendering subtitles). The only usage hint is the default family behavior, which is parameter semantics rather than selection guidance.

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