whoami

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: it fails with instructions when the sign-in has expired, and its environment selection defaults to the first entry in the allowlist rather than the schema's literal `default: ""`. These are exactly the operational details an agent needs. No contradiction with annotations (read-only aligns with a whoami-style query).

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?

Three sentences, each earning its place: purpose, failure behavior, and parameter semantics. No filler or repetition of schema/annotation content. Slight deduction for the awkward, fragment-like first sentence ('Who pac is signed in as...') and the minor punctuation/formatting quirks, but overall it is tight and well-ordered.

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?

This is a simple tool — one optional parameter, no output schema, no nested objects — and the description covers purpose, the key failure mode (expired sign-in), and parameter semantics. The only real gap is that with no output schema, the return shape is never described, but for a whoami-style tool the output is predictable enough that this is a minor omission rather than a blocker.

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 0%, so the description carries the full burden for the `environment` parameter, and it delivers: it explains the value domain (URL or id), the source (the allowlist), and the effective default (first from allowlist) — which usefully corrects the misleading `default: ""` in the schema. It doesn't fully specify URL/id format or how to discover the allowlist, so a 5 is not warranted.

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 states a specific purpose: reporting which identity PAC is signed in as and which org it reaches within an allowlisted environment, with the `pac env who` mapping. This is clear and distinct in intent from siblings like list_environments (which lists environments, not identity) and pac_status (tool status). It earns a 4 rather than 5 because it never explicitly names a sibling or states the demarcation line, and the phrasing of the first sentence is somewhat awkward.

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 context is implied rather than explicit: the tool answers 'who am I / which org am I reaching' before working in an allowlisted environment. It provides parameter-level guidance (environment = URL or id from the allowlist, default first) but gives no when-to-use vs. alternatives guidance, no exclusions, and no mention of when pac_status or list_environments would be the better choice. This matches '3=implied usage'.

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