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

Beyond the annotations, it discloses that the selection is sticky for the session and, critically, the precedence rule relative to a project pin ('may narrow a project pin but never overrides it to another project'). That precedence behavior cannot be inferred from the annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false). It stops short of describing what happens on an invalid or unknown id.

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 sentences, no filler, with the core action and the parameter preference front-loaded before the precedence caveat. Every clause carries information an agent needs.

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 session-scoped setter with no output schema and full annotation coverage, the description covers mutability, scope, parameter preference, and precedence. Only edge behavior (invalid id, effect on subsequent calls) is left unstated, which is a minor gap.

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 100%, so baseline is 3, but the description adds meaning the schema lacks: instance_id is the preferred input and project_name is the fallback, while the schema calls them merely alternatives. The 'unique project_name' requirement adds a validity constraint as well.

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 ('Set') and resource ('sticky engine instance') and scopes it to 'this MCP session', which is precise enough to separate it from list_engine_instances. It does not explicitly name the sibling tools, so differentiation is inferred rather than stated.

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 gives selection guidance between the two parameters ('instance_id (preferred) or a unique project_name'), which is useful. However, it never says when to use this tool at all, nor when to call list_engine_instances first to obtain an id, leaving the workflow implied.

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