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

With no annotations, the description carries the full behavioral burden. It discloses that this is a read-style lookup, that it is free, and what data comes back, but says nothing about not-found behavior, whether lookups require auth, or rate limits.

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?

A single front-loaded sentence that states the lookup key, the resource, and the return contents with zero filler. The trailing 'Free' is a compact, genuinely useful cost signal.

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 one-parameter read tool with no output schema, the description compensates well by enumerating the fields returned. The remaining gap is error/not-found behavior for an invalid agentId or slug, which an agent would need when a lookup misses.

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% and the schema already explains that ref is an agentId number or 12-character draft slug. The description repeats that same information rather than adding format, validation, or fallback guidance beyond the schema.

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?

The description gives a specific verb ('Look up') plus a precise resource ('Arc Agent Passport') and enumerates the returned facets (registration file, owner, endpoints, active flag, links). That clearly separates it from the mutation siblings arc_passport_draft/buy/confirm and from arc_agent_status, though it never names those siblings explicitly.

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?

Usage is only implied: a lookup tool taking an agentId or draft slug. The one explicit usage fact is 'Free', which tells the agent there is no cost barrier. There is no statement of when to prefer this over arc_agent_status or arc_agent_search, and no prerequisites.

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