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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds real context beyond that: the response includes every stored attribute, and it flags the result as PERSONAL DATA governed by the same handling rules as list_contacts. The PII rule is only by reference, and nothing is said about not-found behavior, 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?

Two sentences, zero filler. The payload description and the id-provenance pointer are both front-loaded, and the PII warning is a short trailing clause rather than a paragraph.

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?

With no output schema, the description carries the return-value burden and does so by enumerating the returned fields. Combined with annotations covering safety, an agent has what it needs to call this correctly; only not-found/error behavior and the site_id scoping are unaddressed.

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 100%, so site_id, contact_id and user_goal are already documented, and the schema itself notes contact_id comes from list_contacts. The description reinforces the id lookup but adds no format or scoping detail beyond the schema, so 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 ("Fetch a single contact by id") and enumerates exactly what comes back (name, email, phone, company, address, pipeline stage, tags, custom fields, lead score, owner). It also names the sibling that produces the id, so the agent can distinguish it from list_contacts without opening the 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?

"Get the id from list_contacts" gives the concrete prerequisite and implicitly routes single-record retrieval here versus the list tool. It stops short of an explicit when-not-to-use or of naming any other alternative (e.g. get_contact_journey, list_owned_records) for related needs.

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