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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the mutation risk is known. The description adds meaningful non-obvious behavior: existing same-named fields are overwritten while others are added, and it returns a count of updated records. It stops short of stating auth requirements or partial-failure behavior, so not a 5.

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 sentences, front-loaded with purpose then mechanics; each sentence carries information. Slightly longer than strictly necessary since the array/targeting sentence partly echoes the schema, but there is no filler.

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 bulk mutation with 100% schema coverage and no output schema, the description covers when to use it, how to target records, overwrite semantics, and the return value. The analytics-only parameters (context, llm_model, conversation_id) are fully documented by the 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 the schema already documents id, externalId and the {fieldName: value} map. The description restates the id-or-externalId targeting and field map without adding syntax or format detail beyond the schema, so 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?

States a specific verb+resource+scope ('Set custom fields on MANY records in one call') and names the single-record sibling it replaces (set_custom_field). An agent can distinguish this from every other sibling without opening a schema.

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?

Explicitly says when to use it ('to tag or score an entire dataset after analysis') and names the alternative with the condition that selects it ('instead of calling set_custom_field once per record'). No inference required.

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