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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real behavioral value by explaining that omitted fields are untouched and that null (or an empty reviewers array) is the clearing signal — non-obvious semantics for a mutation tool. It stops short of saying what an invalid state name or unknown label does, and its implied repeat-safety sits slightly awkwardly with idempotentHint=false.

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, then the partial-update rule, then the clearing convention. Nothing is padded or repeated.

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 14-parameter mutation tool with no output schema, the definition covers the two things an agent most needs: which fields are optional-by-omission and how to unset values. It does not cover permission requirements, side effects such as notifications, or validation failures, which leaves modest gaps.

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 79% across 14 parameters, so the schema does most of the work. The description still adds cross-parameter meaning by consolidating the null-clears-assignee/project/cycle convention and the empty-array-clears-reviewers case, which no single schema field states outright.

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?

"Change fields on an existing issue" gives a specific verb and resource, and the partial-update semantics separate it from create_issue. It never names bulk_update_issues, move_issue or archive_issue, so the agent has to infer the boundary from the verb alone.

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 description implies when to use it (single-issue field edits) via "Only the fields you pass are touched," but gives no explicit when-not guidance and no routing to siblings like bulk_update_issues for multiple issues or move_to_cycle for sprint assignment.

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