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 the config-file source, which is real context, but says nothing about what gets spawned (ports, processes), reversibility, or failure behavior when run.json is absent. With annotations carrying the safety burden, a 3 fits.

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?

A single front-loaded sentence with no filler; the config path is the only extra detail and it earns its place. Slightly short of 5 because brevity here borders on under-specification rather than precision.

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 one-optional-param mutation tool with no output schema, the description covers what the tool does and where config comes from. It is still missing prerequisites (run.json must exist, project context via use_project), what 'start' produces, and the relationship to set_run_config and stop_preview, which an agent would need before calling it safely.

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 description coverage is 100%: the single optional project_id is fully documented in the schema, including the 'use session from use_project' alternative. The description never mentions project_id, so it adds nothing beyond the schema, and baseline 3 applies.

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?

Names a specific verb ('Start') and resource ('preview services'), and adds the config source '.mythex/run.json' so the agent knows what drives the start. It implicitly contrasts with get_preview and stop_preview, but never names them, so the distinction comes from the verb rather than from explicit differentiation.

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 '.mythex/run.json' reference hints that configuration must exist first, but there is no explicit when-to-use, no prerequisite statement (e.g. run set_run_config/use_project first), and no mention of stop_preview as the counterpart. Usage must be inferred from the verbs in the sibling list.

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