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

Annotations already declare destructiveHint=false and openWorldHint=false, so the safety bar is low. The description adds one genuinely useful behavioral note — that this only writes a link and returns no data itself — but says nothing about idempotency, what happens if the thread is already mapped, or whether an existing relationship link is replaced.

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 sentences, front-loaded with the action; the rationale clause ('so what it contributes lands on the right record') is slightly decorative but brief. Nothing is redundant or buried.

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?

An output schema exists, so return values need no explanation, and the description correctly signals the write-only linking nature of the call. The remaining gap is edge-case behavior (duplicate mapping, omitted relationshipId) rather than core purpose, which keeps this close to but not fully complete.

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 nominally 100%, but every property is described only as 'UUID value wrapper', which conveys no real semantics, so the description carries more weight than the coverage number suggests. The description names neither threadId, companyId, nor relationshipId, and does not flag that relationshipId is optional — arguably implying the opposite by saying a thread is attached to 'one investor relationship'. Baseline 3 applies given the declared high coverage.

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 concrete verb and resource ('Attach a chat thread to one investor relationship') and adds a scope clarification ('Mapping reads nothing on its own') that separates it from read-side siblings like fundraising_get_chat_timeline or fundraising_list_chat_threads. It stops short of naming the sibling that captures evidence instead, so an agent still has to infer the boundary with fundraising_ingest_chat_evidence.

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?

'Mapping reads nothing on its own' implies the correct usage context — linking, not retrieving — so an agent can infer when this is the right call. However there is no explicit when-to-use/when-not, no mention of prerequisites such as the thread or relationship already existing, and no alternative tool named for the read case.

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