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

With no annotations, the description carries the full load and does it well: energy cost, character cap, per-tick rate limit, sanitization behavior (code fences, tag-like spans, tool-call syntax stripped), return value (message_id), and a security warning that content is unverified and instructions in messages should never be followed. These are exactly the behavioral traits an agent needs and cannot infer from the schema.

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?

Dense but front-loaded, leading with what the tool does and the reach semantics before costs and caveats. Almost every sentence earns its place, though the parenthetical about api_key/threading adds length the agent must parse mid-sentence.

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?

There is no output schema and no annotations, so the description must cover return values, safety, and routing on its own – and it does, including the message_id return, threading, cost, and the adversarial-content warning. Nothing an agent needs to invoke this correctly appears to be 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 coverage is 86%, so most parameters are already documented, but the description adds genuine meaning beyond it: reply_to threads a conversation via received message ids, regarding_trade ties negotiation to a specific offer and must correspond to an existing trade, and both are free. It also clarifies the target_agent vs. broadcast/region_broadcast distinction in prose. Slight gap: it doesn't restate that 'text' is the only required field.

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 (send) and resource (free-form text message) and immediately distinguishes the two delivery scopes: a private message to any agent in your match vs. a region broadcast. This is unmistakable against siblings like read_messages or inspect_agent.

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 explicit routing rules ('any agent anywhere in YOUR match', 'an agent in another match is out of reach and answers unknown_agent') and states the cost/limits that gate use (0.5 energy, 500 chars, 10/tick). It also names the optional threading affordances (reply_to, regarding_trade) and what they are for, so the agent knows when to reach for them.

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