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

Annotations carry only destructiveHint=true, so the description must do real work here — and it does: 'Only the fields you pass are changed' clarifies this is a partial/patch-style update rather than a destructive overwrite, which directly softens an aggressive destructive hint. It still says nothing about auth, errors on invalid field IDs, or the encryption-password failure mode (that lives only in the schema).

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 tight sentences: mutation scope, partial-update rule, and endpoint. No filler and the most decision-relevant fact (what gets changed) 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?

With no output schema, the agent doesn't need return-value documentation, and the schema fully covers parameters. For a destructive update tool the description is nearly sufficient, though an explicit note that unlisted fields are untouched (already implied) plus behavior on invalid IDs would close the remaining gap.

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 100% and the schema documents every parameter, including the field-value shapes and encryption_password header. The description adds the partial-update semantic tied to 'fields', but no syntax or format detail beyond the schema, so the baseline of 3 applies.

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+resource ('Change field values on an existing submission') and adds the read/unread variant, which is more than a restatement of the title. It implicitly separates itself from create_submission/get_submission via 'existing submission', but never explicitly names a sibling or an alternative, so it stops short of a 5.

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 by the verb: an agent can infer you call this to modify rather than fetch a submission, but the description gives no when-to-use/when-not guidance, no prerequisites, and no explicit pointer to alternatives (create_submission, get_submission, formstack_list_form_fields).

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