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Guidance for sensitive form fields (credentials, card data, national IDs) in declarative and imperative tools

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
48/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
html
Domain
security

Research direction

Read the declarative API and security guidance, then review related issues #110 and #313 and the linked country-packs design notes. Compare the proposed autocomplete exclusions, agent handoff hint, and security guidance against the spec's existing tool schema. Done means a concrete direction is agreed on and the spec explains how sensitive form fields are handled.

Written by the indexing model from the issue text.

Description

declarative security-tracker

Problem

Neither the spec nor the Chrome security guidance says how sensitive fields should be handled when a form becomes a tool. The declarative API builds inputSchema from every named control, so a checkout form exposes card number and CVV, and a login or KYC form exposes one-time codes and national ID numbers, as agent-fillable parameters.

Browser agents already treat these fields specially: Claude in Chrome, Gemini in Chrome and OpenAI's agent hand passwords, OTPs and payment details back to the user rather than passing them through the model. Tool schemas currently give them no way to know which parameters those are.

Evidence

  • PCI DSS v4.0.1 Req 3.3.1: Sensitive authentication data (CVV, PIN) must not be retained after authorization. We treat agent transcripts as retention.
  • NIST SP 800-63B, PSD2 SCA-RTS Art. 4 and RBI's 2025 authentication directions treat one-time codes as authentication factors held by the user.
  • Several jurisdictions restrict processing of national ID numbers: National laws under GDPR Art. 87, UIDAI rules for Aadhaar, and Singapore's PDPC NRIC guidelines.

In auto-webmcp (an open-source library that turns forms into WebMCP tools) we now exclude these fields from the schema, list them in the description, and set consequentialHint. Design notes: https://github.com/prasanna-gyde/auto-webmcp/blob/main/docs/design/country-packs.md

Possible directions

  1. Declarative API: By default, exclude controls whose autocomplete is cc-number, cc-csc, cc-exp*, one-time-code, current-password, new-password or webauthn from the generated schema.
  2. Signal to agents: A per-parameter hint (for example x-user-input: true, or a list on the tool) meaning "the user completes this field", so agents hand off instead of guessing or asking for the value in chat.
  3. Security considerations: A short section recommending that tool results not echo credentials, card data or hidden inputs.

Related: #110 (sensitive tool outputs; a comment there raises the input direction this issue covers) and #313.

Happy to contribute text or test cases.

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