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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is already covered. The description adds valuable behavioral context beyond that: it tells the agent that the response shape matches envelopes_list and that a 404 occurs when the envelope is not bound to the calling agent instance, which is exactly the kind of behavioral nuance that an agent needs to be prepared for.

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?

The description is three concise sentences: the first clearly states the primary action, the second provides the return shape, and the third gives an edge-case. No fluff, each sentence earns its place, and the most important information is front-loaded.

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 simple one-parameter getter with no output schema, the description is complete. It communicates the primary use, the return shape, and the key 404 error scenario. The annotations already cover safety and idempotency. Nothing critical is missing for an agent to call this tool correctly and handle the outcome.

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?

The schema description covers the envelope_id parameter fully with a clear 'description' field. The tool description mostly repeats the 'by id' notion but does not add semantic meaning beyond the schema. The parameter is simple and well-documented in the schema, so the description doesn't need to compensate.

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 clearly states a specific action (fetch), a specific resource (a single envelope), and the identifier used (id). It distinguishes itself from its sibling envelopes_list both in particle size (single vs. list) and by referencing the same return shape, so an agent can tell them apart immediately.

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?

The description gives clear context: use this to retrieve one envelope by ID. Although it doesn't explicitly say 'use envelopes_list for multiple envelopes', the single-by-id framing strongly implies the correct condition. Not having an explicit alternative is a minor omission, but the intended scope is obvious.

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