Spell Word

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

Annotations already declare the tool as read-only, idempotent, and non-destructive. The description adds the return format (array of characters, indexed list) which provides useful context beyond annotations, but does not disclose additional behaviors like rate limits or authentication needs.

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 very concise: two short paragraphs plus a clear args list and example. Every sentence serves a purpose, and the main action is front-loaded. No wasted words.

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 simple tool with only two parameters and full annotation coverage, the description provides enough context. It explains the return format and includes an example. Minor gap: the description could clarify the exact return structure when include_indices is false.

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?

Input schema coverage is 100% and the description repeats the parameter descriptions without adding significant new meaning. The example usage provides some context, but the baseline is appropriate as the schema already documents the parameters adequately.

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 clearly states the tool's action: 'Break text into individual characters with optional indices.' This is a specific verb-resource pair that distinguishes it from sibling tools like char_at (single character) or count_letters (counting).

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 says 'Perfect for verifying character-by-character content,' which provides clear context for when to use it. However, it does not explicitly mention when not to use it or provide exclusion criteria relative to similar tools.

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