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

Annotations already declare readOnlyHint=false, openWorldHint=true, and idempotentHint=true. The description adds a useful retry-safety mechanism ('same id and text returns the original message') beyond the annotation's binary idempotency hint. However, it does not disclose other behavioral traits like error conditions (409), rate limits, or what exactly the mutation affects beyond the abstract 'adds a message.'

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, front-loaded with the core action and followed by the key retry-safety guarantee. Every sentence earns its place with no wasted words.

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?

Given a mutation tool with three required parameters, rich schema descriptions (100% coverage), and no output schema, the definition provides enough for an agent to invoke the tool correctly. It omits explicit mention of the optional conversation_token and error responses, but those are fully covered in the schema. A slightly richer description could have noted the relationship to continue_conversation.

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 the schema already documents all four parameters in detail, including the idempotency key pattern and the conversation_token omission rule. The description only restates the idempotency guarantee already present in the schema, adding no new parameter semantics. Baseline 3 applies when the schema does the heavy lifting.

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 uses a specific verb and resource: 'Adds a message to your conversation.' It is immediately clear what the tool does. However, it does not explicitly differentiate from the sibling tool continue_conversation, which likely also adds messages, so it falls short of the top score for sibling differentiation.

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?

No guidance is given on when to use this tool versus alternatives such as continue_conversation or start_conversation. The only contextual statement concerns idempotency, which is not usage guidance. An agent must infer the selection criteria from sibling names alone.

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