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

The description discloses three concrete side effects: moving to canceled state, recording the duplicate_of relation, and transferring subscribers. These go beyond the annotations (which only indicate destructiveness and idempotency), giving the agent real behavioral expectations. It does not contradict any annotation.

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?

Two tight sentences: the first states the core action, the second lists the relevant consequences. Every word contributes; no filler, no repetition of already-known tool names.

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 two-parameter mutation with no output schema, the description plus annotations cover what the tool does, what changes, and which parameters are needed. It does not mention edge cases like self-duplicates or pre-existing relations, but that is beyond the expected minimum for this tool.

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?

The schema already documents both parameters as 'duplicate issue identifier' and 'survivor issue identifier' with 100% coverage. The description restates these roles without adding new format, constraint, or usage detail, so it stays at the schema-coverage baseline.

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 uses a specific verb ('Mark'), resource ('an issue'), and target ('as a duplicate of another issue'), which clearly distinguishes it from siblings like delete_issue, update_issue, or set_relation. The first sentence alone specifies the exact action and objects involved.

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 the use case: when one issue is a duplicate of another. It does not explicitly exclude alternatives like set_relation or delete_issue, but the context is clear enough that an agent would not confuse it with those. No explicit when-not guidance is provided, so it stops short of a 5.

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