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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds only that a single record is returned; it says nothing about what happens when the Id is unknown or whether the result is scoped to the connected company.

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?

One sentence, front-loaded with the verb, resource, and lookup key. The conditional clause at the end is slightly muddled but short and does not bury the core action.

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 simple single-record read with full schema coverage and annotations carrying the safety profile, the description is nearly sufficient. The absence of an output schema means return shape is undocumented, but that is a minor gap for a straightforward getter.

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 both the required 'id' and the optional 'company' are already documented in the schema. The description's 'by Id' adds nothing beyond that, 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?

The description states a specific verb and resource ('Get a single vendor credit') plus the lookup key ('by Id'), and the word 'single' distinguishes it from the sibling search_vendor_credits which returns collections. It stops short of naming the sibling explicitly, so it is clear but not fully differentiated.

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 trailing clause 'when no search or write answer already holds it' implies the agent should prefer a search or write response if one is available, which is a usable routing hint. However it never names search_vendor_credits and the phrasing is awkward enough that the condition is inferred rather than stated.

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