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

With no annotations supplied, the description carries the full burden and does so well: it discloses the 2 MB cap, that every table is carried over unchanged, that the output is re-read and its table digest compared to the source, and that the font's OS/2 embedding bits are checked first so a restricted font fails and returns nothing. These are exactly the behavioral traits an agent cannot get from the structured fields.

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?

It is front-loaded and generally well organized, but the opening list "TTF/OTF, WOFF and WOFF2 containers" is immediately restated as "between the sfnt (.ttf/.otf), WOFF and WOFF2 containers," so the first sentence does not fully earn its place. The second half (verification and embedding check) is dense and useful.

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 conversion tool with no output schema, the description covers input constraints, conversion guarantees, verification, and failure behavior. It stops just short of describing the shape of a successful result (e.g., that it returns the converted base64 and/or the digest), which is the one remaining gap.

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 100%, so both parameters (fontBase64 with its length bounds, and the to enum) are already fully documented in the schema. The description restates the base64/2 MB constraint and the container list rather than adding new meaning such as what a successful return value looks like; baseline 3 for high coverage applies.

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 names a specific verb and resource ("Repackages a font you supply as base64 ... between the sfnt (.ttf/.otf), WOFF and WOFF2 containers") and enumerates both the accepted inputs and the target formats. An agent can distinguish this from the font-* siblings (coverage, face-css, glyph-svg) 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?

It states the operating context clearly: "for an agent or build step that needs a web font in a particular format." It also implies the exclusion of .ttc collections via the parameter text, but gives no explicit when-not guidance or named alternative tools, 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.