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

Annotations already declare readOnlyHint and closed-world, so safety is covered; the description still adds real value with 'Free' (cost profile), deterministic ordering ('oldest first'), and the null-thread empty state. It does not cover pagination or size limits for large threads, which keeps it from a 5.

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?

Three compact sentences, front-loaded with the return payload, then the usage trigger, then the edge case. Every sentence carries distinct information with no restatement of the name or annotations.

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, so the description must carry the return shape, and it does: the fields returned, the message/event inclusion, and the ordering. For a two-parameter read tool with full annotation and schema coverage, nothing an agent needs to invoke or interpret it is 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 description coverage is 100% and both parameters (creatorId, campaignId) document their own provenance, so the schema does the work. The description only implies the pairing of campaign plus creator and adds no format or sourcing detail beyond the schema. Baseline 3 applies.

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 ('Returns the email thread with a creator in a campaign') and then enumerates the contents: stage, waiting-on, next action, agreed facts, messages and events. An agent can distinguish this read tool from siblings like send_email or get_creator without opening any schema.

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?

Explicitly routes usage: 'Check it for replies after send_email,' which ties this tool to a concrete workflow moment. It also warns that the thread is null until the first email is sent, avoiding a false-empty reading. No explicit when-not or alternative tool is named, so not a 5.

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