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

Annotations already declare this is a non-read-only, idempotent, non-destructive write, and the description adds genuinely new behavioral context: a hard cap of 10 assignees per thread, the constraint that only users who can read the repository are eligible, the required 'repo' scope and write access, and a partial-failure model via the `skipped` array with reasons. This goes well beyond what the annotations carry.

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?

The operative verb and the remove-mode qualifier are front-loaded, followed by eligibility rules, parameter guidance, auth requirements, and return shape in a logical order. It is a dense single block rather than cleanly separated lines, and the migration note is slightly tangential, but no sentence is wasted.

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 7-parameter mutation tool with no output schema, the description covers the operation, both modes, eligibility limits, auth requirements, and even the response shape ({assigned, skipped, removed, assignees}). An agent has everything needed to call this correctly and interpret partial success.

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 only 57%, and the description compensates meaningfully: it explains that `assignee` is one username while `assignees` is the array alternative, that `type` defaults to 'issue', and that `remove` inverts the operation. It does not spell out `owner`/`number`, but those are conventional and required, so the added meaning is proportionate.

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 names a specific verb+resource combination (assign/unassign users on an issue or pull request) and covers both modes in the first clause. The note that the old `assignee:<username>` labels were migrated distinguishes this from the label-based sibling tools (merjax_label_issue / merjax_unlabel_issue) without needing to open 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?

It clearly states the condition that selects each mode (assign by default, unassign with remove: true) and gives the prerequisites ('repo' scope and write access). What it lacks is an explicit pointer to a named alternative sibling, but the migration note about labels effectively tells the agent not to use label tooling for assignees.

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