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

Annotations fully declare the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description is not obligated to restate them and does not contradict them. However it adds nothing beyond those structured hints—no note on what the returned definition contains or error behavior for a bad ID.

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 short sentence with no filler and the key scope information front-loaded. It is appropriately sized for a one-parameter lookup, though it is so terse that nothing beyond the bare action is conveyed.

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 by-ID getter with 100% schema coverage and full read-only annotations, the description covers what an agent needs; the absent output schema means return values need not be explained. Only the lack of any usage routing to the sibling list tool keeps it from being fully complete.

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% with a single UUID-typed id, so the schema already documents the parameter fully. The description only paraphrases 'by ID' and adds no format or validity detail beyond the schema, making the baseline of 3 appropriate.

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 (Get) and resource (custom field definition) scoped to a single record by ID, which implicitly separates it from the plural list_custom_field_definitions sibling. It never names a sibling explicitly, so differentiation relies on the reader inferring singular-vs-plural.

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 statement of when to use this versus list_custom_field_definitions, get_custom_field_value, or any other retrieval sibling, and no preconditions are given. The only hint is the word 'single', which the agent must interpret on its own.

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