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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the appended 'Read-only' adds nothing new. The valuable addition is the enumeration of returned state fields, but there is no mention of error behavior for an unknown or expired envelope id, which is the real unknown for a lookup tool.

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 payload-bearing field list and no filler. The trailing 'Read-only' is the only wasted clause since annotations already say so.

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 are formally documented and the description needn't recapitulate structure, yet it helpfully names the key fields. For a single-parameter read tool with full annotation coverage, only the missing sibling routing and error-case note keep it from being 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?

One required parameter with 0% schema description coverage, so the description would need to carry the meaning of envelope_id. It implicitly establishes that an envelope is an identifiable object with a state, but does not state the id's expected form or provenance (where the agent obtains it).

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 ('Return an envelope's state') and immediately enumerates the exact fields returned (budget, cap, calls used, spent, remaining, allowlist, expiry), which distinguishes it from mutating siblings like kill_envelope and open_envelope. An agent can tell what this does 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?

Usage is implied by the read-only framing and the field list, but the description never names check_spend or explains when to inspect an envelope versus when to check spend or apply policy_rules, which is the most likely routing ambiguity among the siblings.

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