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

The description reveals behaviors annotations do not convey: the stats secret is returned once and unrecoverable, only its hash is stored, no registration occurs by default, registration failure is only a warning, and editing a variant creates a new test with empty history. These are exactly the non-obvious traits an agent must know. There is no conflict with the 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?

Four topically organized paragraphs: core promise, variants-vs-slots, registration/identity, and secret lifecycle. It is long, but every sentence carries a caveat or decision that would otherwise be missing, and the most important return semantics are front-loaded. This is appropriately sized for a 9-parameter tool with nested objects.

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 high-complexity tool with rich schema and output schema, the description covers the critical hidden behaviors: one-time secret, identity hashing, registration warning, and test replacement on edit. The one notable gap is that it never explicitly states that at least one of variants or slots is required, despite the schema listing zero required parameters. Because of that, an agent could attempt a meaningless empty build.

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?

The input schema already covers 100% of parameters, so the baseline is 3; the description adds conceptual meaning by framing slots as combination optimization, variants as single-element control tests, and publishableKey as an optional registration side-effect. It also clarifies that the config/URLs are the test and identity is a hash, which gives semantic weight to name, variants, and context. It does not duplicate schema field descriptions, which is appropriate at full coverage.

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 first sentence names the operation (creates), the object (LiveVariant test), and the payload (URLs + stats secret), which is immediately informative. The later paragraphs clarify the no-registration default and optional publishableKey registration, so it can be told apart from a pure registration tool. It never explicitly names a sibling alternative, so it stops short of full 5.

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 explicit selection guidance for variants vs slots, explaining when each is appropriate and that both run the same joint model. It also states the exact condition for registration (pass publishableKey on an account-enabled deployment) and that failure degrades to a warning. It does not enumerate alternative sibling tools or state a when-not-to-use condition, so it lacks explicit exclusionary guidance.

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