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

The annotations already declare this as a non-read-only, non-idempotent, open-world write, so the safety profile is covered. The description adds a genuinely non-obvious behavioral constraint beyond that: if the sender is outside the team, nothing private may be shared without the owner's approval. It does not describe delivery guarantees or what happens on repeated invocation, but the added policy context is substantive.

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 short sentences, zero filler, with the core action front-loaded and the risk caveat second. Every clause earns its place and nothing is repeated from the schema.

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 five-parameter write tool with full schema coverage, an outcome enum, and safety annotations, the description covers purpose and the main privacy risk. The remaining gap is sibling differentiation against reply_thread and similar messaging tools, which the description never addresses.

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%, including a fully documented outcome enum and ownerNote semantics, so the schema carries the parameter burden. The description only echoes the taskId link ('from read_messages') which the schema already states. Baseline 3 is appropriate since nothing new is added about parameters.

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 gives a specific verb and resource: 'Answer a message you received (by its taskId)'. An agent immediately knows this sends a response to an existing message rather than creating one. It does not differentiate itself from likely siblings such as reply_thread or post_message, so it stops short of a 5.

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?

Usage is implied: this is the tool for answering a message you already received, and the taskId reference points back to read_messages. There is no explicit statement of when not to use it, nor any named alternative for thread replies versus direct replies. The privacy caveat functions partly as a precondition but is not a usage rule in the routing sense.

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