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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the bar is lower, yet the description still adds value by disclosing the composition of the result — tags, attributes, and subscription/block state. It does not say what happens when the id does not exist (error vs null), which is the main remaining gap.

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 with no filler: the primary behavior is front-loaded, and the disambiguation sentence follows. Every clause carries information an agent would otherwise have to guess.

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?

For a single-resource read-only getter with one parameter, the description covers purpose, alternative, and the salient contents of the response — important given there is no output schema. Missing only failure-mode behavior (not-found response) and any note on what the returned attributes are keyed by.

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?

Only one parameter exists and schema description coverage is 0%, but the property name contact_id plus the phrase "by id" already make the meaning unambiguous. The description adds no detail on id format (prefixed ID, UUID) or source, so it does not compensate for the empty schema description.

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 ("Read one contact by id") and immediately scopes what is returned (tags, attributes, unsubscribed/blocked state). It also names the sibling it is not — search_contacts — so an agent can distinguish it from the lookup-family tools without opening a 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 alternative with its triggering condition: looking up by email routes to search_contacts with the email parameter. It does not cover adjacent cases (contact activity, enrollments, tags-only listing), so the routing is clear but not exhaustive.

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