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

Goes well past annotations by disclosing the highest-risk behavior: all provided fields are set wholesale and an empty value CLEARS the setting. It also states the hostname is immutable and that these tools cannot delete or move a domain, which is exactly the sort of consequence an agent needs before calling a destructive tool.

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?

Front-loads the purpose and mutable fields, then layers on behavioral caveats. Every sentence contributes, though the front-door example makes the middle dense and a bit longer than strictly necessary.

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?

An output schema exists, so return values needn't be explained. The description covers mutability, clearing semantics, immutability of the identifier, and the out-of-scope delete — everything an agent needs to invoke this destructive tool safely.

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?

Schema coverage is 100%, so the baseline is 3, but the description adds relational meaning the schema doesn't: shop.customer.com/<path> serves <slug_prefix>/<path>, and root_endpoint is relative to slug_prefix. That clarifies how the parameters interact, though it doesn't add per-parameter syntax detail beyond the schema.

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?

Names a specific verb (update) and resource (custom domain) and enumerates exactly which settings are mutable (display_name, slug_prefix, root_endpoint). It also states what is not mutable (hostname) and rules out deletion, which separates it from create_custom_domain, get_custom_domain and the delete_* siblings.

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?

Explains the concrete use case — making a domain the public front door of an app — with a worked example of how slug_prefix and root_endpoint combine. It also routes deletion elsewhere ('removing a claim is done in the Tessryx app'). It stops short of an explicit 'use this instead of X when Y' against create_custom_domain.

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