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

Annotations indicate non-read-only, non-open-world, and non-idempotent behavior, but the description adds valuable context beyond these flags: 'Secure — no filesystem access, no network,' 'Requires API key,' and the return format. This discloses security boundaries and auth requirements without contradicting 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 concise and well-structured, with five tightly-packed sentences each adding value: core action, use cases, security, return format, and authentication. There is no redundancy or filler.

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 tool with only two parameters and no output schema, the description is remarkably complete. It covers purpose, use cases, security constraints, return shape, and API key requirement, leaving no critical gaps for an agent to select and invoke it 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?

With 100% schema coverage, the input schema already fully documents both parameters, including examples for 'code' and an enum with defaults for 'language.' The description reinforces the available languages but adds no additional parameter-specific semantics beyond what the schema provides.

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 purpose with a specific verb and resource: 'Execute JavaScript or Python code in an isolated sandbox.' It also lists concrete use cases (data processing, math, CSV parsing, etc.), and no sibling tool offers code execution, making it easily distinguishable.

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 provides an explicit 'Use for' list covering common coding tasks, giving clear when-to-use guidance. It does not mention exclusions or alternatives, but since no sibling tool performs code execution, explicit alternatives are unnecessary.

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