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

readOnlyHint=true already tells the agent this is a safe read. The description adds genuinely useful context by mapping "customer" to the Swell `accounts` model and giving the backend route, but says nothing about error behavior (e.g. missing id) or the shape of what comes back.

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?

Three short sentences, front-loaded with the core action and id requirement, followed by optional-parameter support and the underlying endpoint. Nothing is wasted.

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 single-resource read with full annotation coverage and full schema coverage, the description covers purpose, optional params, and the model/endpoint mapping. Only the return shape and not-found behavior are unstated, and the latter is a minor gap given the absence of an output schema.

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 description coverage is 100%, so all three parameters are already documented in the schema with an example for `expand`. The description only restates that `expand` and `fields` are supported, adding no syntax or semantics 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?

States a specific verb and resource ("Fetch a single customer ... by id") and clarifies the underlying model name (`accounts`) plus the REST route. The word "single" implicitly separates it from the sibling `swell_list_customers`, but the sibling is never named, so the differentiation is inferred rather than stated.

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?

Usage is implied: retrieve one customer when you already have an id. There is no explicit guidance on when to prefer this over `swell_list_customers` or `swell_query`, and no note about what happens for an unknown id.

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