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

No annotations are provided, so the description carries the full behavioral burden. Beyond noting the target must be a 'running session', it says nothing about whether the call blocks, whether it queues behind an in-flight turn, permission requirements, or failure modes for a non-running session.

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 and the key scope qualifier ('running session') placed where it matters. It is efficient, though arguably too terse for the information the 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?

An output schema exists, so return values need not be explained here. For a two-parameter tool that is nearly acceptable, but the absence of any parameter documentation and of routing guidance relative to run_agent/wait_for_session leaves real gaps.

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 0% for both parameters, so the description should compensate but does not. It never clarifies what 'message' should contain (role, format, whether it is delivered mid-turn) or what form 'session_id' takes or where it comes from.

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 states a specific verb and resource ('Send a follow-up message') and scopes it to 'a running session', which separates it from siblings like run_agent (which starts a session) and wait_for_session. It does not explicitly name those siblings, so differentiation is inferential 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?

'Follow-up' implies this is for continuing an already-running session rather than creating one, which is useful implicit guidance. However, it gives no explicit when-to-use versus run_agent, no prerequisites (e.g., that the session must be awaiting input), and no exclusions.

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