start_session

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

Annotations only declare it is a non-read-only, non-destructive, closed-world operation; the description goes well beyond that by guaranteeing isolation in both directions ('nothing in it reaches the desktop... nothing of theirs reaches it') and by describing the return payload, including partial-failure reporting ('anything it couldn't seal'). No contradiction with destructiveHint=false or openWorldHint=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 sentences, front-loaded with the core verb and the isolation guarantee, then the return shape, then the lifetime. The prose is slightly literary ('a sound server whose sink plays to nowhere' style is confined to the schema), but every sentence carries distinct information with no filler.

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?

With 15 parameters, no required fields, and no output schema, the description carries exactly the right load: it explains the isolation model, the lifetime, and what the returned answer contains, including what it could not seal. Nothing an agent needs to invoke or interpret this call is missing.

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%, so all 15 parameters are already documented with formats, defaults and examples (WIDTHxHEIGHT, ISO 8601 clock, USER@HOST identity, loopback-only net). The description adds no parameter-level meaning beyond the schema, so the 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?

States a specific verb and resource ('Start a sealed session') and immediately defines what 'sealed' means: its own X11/Wayland display, its own D-Bus and accessibility bus, and a scratch home. This is unmistakably distinct from stop_session and from the action tools that operate inside a session.

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 lifecycle is spelled out implicitly but clearly: the session is what spawn_program starts programs in, and it lasts until stop_session. That gives the agent enough context to know this must precede the spawn/observe tools, though it states no explicit when-not or prerequisite conditions.

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