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

Beyond the readOnly/closed-world annotations, the description discloses the return payload (blocks with counts and samples, scripts needed, per-family coverage, gaps with a suggested Noto family, Han unification and RTL notes) and, importantly, its epistemic limits — coverage comes from general font knowledge and varies by version/OS, unknown fonts are flagged unknown, and nothing is rendered. That caveat is genuinely useful context the annotations don't carry.

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?

Front-loaded with the core purpose and output shape, then caveats. It is a dense single block with semicolon chaining that is slightly hard to scan, but every clause (Noto recognition, Han unification, version variance) contributes.

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?

With no output schema, the description fully carries the return-value burden, describing each output section and the reliability caveat. For a two-param analytical tool, an agent has enough to call it and interpret results correctly.

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% and both parameters are already documented with examples, so the schema does the heavy lifting. The description restates the pass-text/optional-fonts pattern without adding format or constraint detail beyond what the schema provides, so baseline 3 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?

States a specific verb and resource ('Maps text to scripts using a built-in Unicode block table') and enumerates the script families covered, so it is clearly distinct from siblings like check_cjk_line_breaking or localisation_readiness. An agent knows exactly what this tool produces.

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 says to pass `text` and optionally `fonts`, which implies the invocation pattern, but never states when to reach for this tool versus localisation_readiness, check_cjk_line_breaking, or plan_text_expansion. Usage context is implied only.

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