string_substring

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

The description does not disclose behavioral traits beyond the basic function. It does not mention behavior for out-of-bounds indices, default handling of the end parameter, or any side effects. With no annotations, the description fails to provide necessary context for safe usage.

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 extremely short (two words), but it is under-specified rather than concise. It lacks critical details that could be included without verbosity, such as the use of numeric indices.

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 the complexity of a substring operation with optional parameters and no output schema, the description fails to explain return values or edge cases. It is not complete enough for an agent to reliably use without additional knowledge.

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?

Since the input schema provides complete descriptions for all three parameters, the description adds no additional meaning. The baseline of 3 is appropriate because the schema already covers the semantic information.

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 'Extract a substring' states the action and resource clearly, but it is too generic given the many sibling tools like regex_extract. It does not specify that it uses numeric indices, which could lead to confusion with pattern-based extraction.

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?

No guidance is provided on when to use this tool versus alternatives like regex_extract, string_slice, or other extraction methods. There are no prerequisites or exclusions mentioned.

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