send_vdi_session_message

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

Goes beyond the annotations by disclosing blast radius ('low', 'informational only, no session disruption'), the absence of a confirmation gate, and that calls are audited. These are real behavioral traits an agent cannot infer from destructiveHint=false/readOnlyHint=false alone. It does not describe failure behavior or what happens if no matching sessions exist.

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?

Four short, front-loaded sentences led by a [WRITE] marker and an example. No filler; each clause conveys distinct information (purpose, safety, targeting, audit).

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 5-parameter, single-required-field write tool with no output schema, the description covers purpose, targeting, safety profile, and audit trail. Remaining details (message_type values, target config resolution) are already documented in the schema.

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 already 100%, so the baseline is 3. The description adds value by clarifying the alternative targeting semantics ('session_ids OR user'), which the per-parameter schema text does not express as an either/or choice.

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 (send a message to Horizon sessions) and reinforces it with a concrete example ('save your work, maintenance in 10 min'). It is clearly distinguishable from destructive siblings like logoff_vdi_session or disconnect_vdi_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?

Gives clear targeting guidance ('Identify by session_ids OR user') and explains there is no confirm gate because the action is informational. It does not explicitly state when to prefer this over alternatives such as logoff, but the usage context is clear enough to act on.

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