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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=true, so the safety profile is covered. The description adds real context beyond that: upsert semantics (create-or-update), the null-to-clear behavior that explains the destructive hint, and an explicit write-access requirement. It does not explain error behavior when the field definition is missing.

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 action and scope, followed by the clearing behavior and the permission requirement. No filler or redundancy.

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?

Covers the mutation, upsert, clearing, and auth prerequisite for a 4-parameter mutation tool with no output schema. Missing only edge-case behavior (undefined fieldId, invalid entityType) which an agent might need for error handling.

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 75%, so most parameters are already documented in the schema (including 'New value, or null to clear'). The description largely restates the null-clearing semantics and adds entity-type scoping, without new syntax or constraint detail — baseline 3 is 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 and resource ('Set (upsert) a custom field value') and enumerates the target entity types (task, project, proposal). It does not explicitly name the sibling set_bulk_custom_field_values, so differentiation from the bulk variant is left to inference from 'a custom field value' (singular).

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?

Provides operational usage detail — pass value: null to clear, and caller must have write access — but never states when to prefer this over set_bulk_custom_field_values or update_* tools. Usage is implied by the singular, single-entity framing rather than stated.

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