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

The description goes well beyond the readOnly/idempotent annotations by disclosing that the operation is deterministic, free, and has no character quota, and by explaining the output mechanisms (dir spans, Unicode isolates, LRM/RLM marks). It also clarifies the ordering problem it solves, giving agents a concrete model of the transformation. No contradiction exists between the description and annotations.

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 is information-dense with every sentence earning its place: purpose, format alternatives with renderer guidance, base-direction note, and a determinism/no-quota reassurance. It is front-loaded with the core behavior and avoids repetition of the input schema.

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?

Given three parameters and an output schema, the description covers the essential invocation details: text scope, renderer-specific format behavior, and the rtl base case. The main gap is the meaning of base: 'auto', which is left to the schema default and is not clarified in prose.

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 the baseline is 3, but the description adds genuine value beyond the schema: it explains what the format enum values produce in practical renderer terms and specifies when to pass base: 'rtl' for Hebrew lines that start with a Latin term. It enriches the meaning of text as well by listing example left-to-right units. Auto behavior for base is not explained, which keeps this from a 5.

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: 'Make one mixed Hebrew/English display line render correctly' and explains the exact transformation: keeping left-to-right units whole and in order so nothing is reversed inside a Hebrew line. This clearly distinguishes it from sibling tools like translate, detect_language, or analyze_direction, which address different tasks.

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?

The description gives clear context for when to use the tool: whenever a mixed Hebrew/English display line needs correct visual ordering. It also provides strong format-selection guidance (html for web, isolate for modern engines, marks for older Android) and tells when to pass base: 'rtl'. It does not explicitly mention exclusions or compare against sibling tools, but those tools are functionally distinct enough that the usage context is clear.

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