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

Annotations already declare readOnlyHint=false and destructiveHint=false, so safety is covered. The description usefully discloses that a call returns an in-flight build rather than always starting a new one, which is real behavioral context. However that 'reuse existing build' behavior sits in mild tension with idempotentHint=false, and nothing about auth requirements or build lifecycle/status is disclosed.

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?

A single tight sentence with zero filler, and the primary action (build the active version) is front-loaded ahead of the fallback clause. Nothing is wasted, though there is little structure to speak of.

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 one-parameter mutation tool with no output schema, the description covers the action but not the outcome: it never says what a caller receives (build id, status, log reference) despite get_sandbox_build_log existing as a sibling. Adequate but leaves a visible gap around return semantics.

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 a single parameter at 100% schema coverage (templateId documented as 'Sandbox id (sbt_...)'), the schema fully carries parameter meaning. The description adds nothing about the identifier's format or source, so the 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 (Build) and resource (the sandbox's active version), and adds a second clause about returning an already-running build. It is clearly distinguishable in intent, though it never names the closely related siblings like activate_sandbox_template_version or save_sandbox_template that an agent might confuse it with.

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?

There is no when-to-use guidance, no prerequisite (e.g., does building require the version to be saved first?), and no condition pointing to alternatives such as activate_sandbox_template_version. The only temporal hint is that an existing running build is reused, which is inferred rather than framed as a decision rule.

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