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

Despite readOnlyHint=true, the description adds rich behavioral context the annotation doesn't: it confirms nothing is written to the workspace, explains that mailbox passwords cannot be exported and thus accounts must be reconnected via OAuth or bulk-uploaded with app passwords, and discloses the important quirk that the backend treats all non-GET calls as writes requiring a read & write API key. This is exactly the kind of non-obvious behavioral detail that goes beyond annotations.

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 front-loaded with the core purpose, then adds necessary operational context. It's a bit dense and packs multiple ideas (read-only preview, password limitation, OAuth flow, API key requirement) into a few sentences, but every sentence earns its place and there's no filler.

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-parameter read tool with annotations already covering safety and no output schema, the description is quite complete. It explains the return artifact (a CSV) and the downstream flow, and covers the API key requirement. It could theoretically mention what the accounts list contains, but the CSV context largely covers that.

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?

With only one parameter and 100% schema description coverage, the schema already documents the instantlyApiKey fully (including where to find it in Instantly's settings). The description adds no additional parameter syntax or meaning. Baseline 3 is appropriate.

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: fetches sending accounts of an Instantly.ai workspace, plus a CSV for Emailchaser's IMAP/SMTP import flow. This distinguishes it from siblings like list_sender_emails (which appears to be the native sender email list) and import_instantly. It's clear what it does, though the dual nature (accounts + CSV) and the relationship to the native list_sender_emails sibling isn't fully clarified.

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 frames the tool as a read-only preview before an import, which implies when to use it. However, it does not explicitly say when NOT to use it or compare it to alternatives like list_sender_emails or import_instantly. The context is implied rather than stated.

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