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

With readOnlyHint and destructiveHint=false already covering safety, the description goes well beyond: it discloses that history is written automatically and can lag, that an empty result means 'never read' rather than 'no reply', and it carefully disambiguates a null seenByThemAt as 'no receipt (or receipts off)' rather than 'unseen'. These are exactly the failure modes an agent would otherwise misread.

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?

Front-loaded with the essential contrast and storage model, and every sentence carries operational weight. The final seenByThemAt passage is long, but it guards against a specific and serious misinterpretation, so it earns its length rather than being padding.

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 legitimately supplies return semantics: ordering (oldest-first), the seenByThemAt receipt field and its null ambiguity, and the write-back behavior. Combined with the 100%-covered input schema, an agent has everything needed to call and interpret this tool.

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 limit, profileUrl, and conversationUrn are already fully documented. The description adds no syntax or format guidance for any parameter; its extra detail is about returned fields (seenByThemAt), not inputs. Baseline 3 applies when the schema carries parameter semantics.

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 ('the saved LinkedIn thread with one person'), including scope ('THEIR messages as well as ours, oldest first') and storage backing ('DB-backed'). It explicitly differentiates from the sibling li_read_conversation, so an agent can choose between them without opening either 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?

Gives an explicit when ('Read this for context before drafting a reply') and a when-not with rationale ('li_read_conversation opens a browser session and takes minutes'). It also spells out the empty-result branch and the recovery action, so the agent knows exactly what to do on each outcome.

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