Remix v2 Forms Code Review#

See remix-v2-forms for canonical patterns. This skill flags violations; the sibling skill teaches the patterns.

Quick Reference#

Issue TypeReferenceManual fetch(), native <form>, wrong <Form> vs useFetcher choicereferences/form-vs-fetcher.mduseState loading flags, useNavigation for per-row, missing pending statereferences/pending-state.mdUnbounded memory uploads, missing encType, unvalidated FormData, mirrored optimistic statereferences/uploads-validation.mdRoute sprawl instead of intent pattern, PUT/DELETE without PE fallbackreferences/multi-action-routes.md

Review Checklist#

• In-app mutations use <Form> or <fetcher.Form>, never fetch() / axios
• <Form> is imported from @remix-run/react (not native <form>) for POST mutations
• useFetcher used when URL should NOT change (row toggle, inline edit)
• <Form> + redirect(...) used when URL SHOULD change (create, delete-then-list)
• Pending state derived from useNavigation() or fetcher.state, never useState
• Per-row pending uses per-row fetcher.state (not page-global useNavigation)
• useNavigation() calls check navigation.formAction to scope to expected path
• Optimistic UI reads fetcher.formData / navigation.formData directly (not mirrored)
• Actions returning success redirect(...), returning json() only for errors / same-page
• <Form encType="multipart/form-data"> on every file-upload form
• unstable_createMemoryUploadHandler always has maxPartSize; large files use disk/stream handler
• FormData values are validated/coerced before reaching the DB (no form.get(x) as string)
• Multiple mutations on one route use intent pattern, not separate routes
• method="put|patch|delete" is documented as JS-only, or rewritten as POST + intent
• nav.formMethod / fetcher.formMethod compared against UPPERCASE strings ( "POST", "GET"); v2's v2_normalizeFormMethod default returns UPPERCASE — === "post" silently never matches.

Valid Patterns (Do NOT Flag)#

These are correct Remix v2 usage and should not be reported:

• <Form> without action prop — posts to the current URL by convention; explicit action is optional.
• GET <Form> — legitimate for search/filter UIs; hits the loader with form fields as URL search params and does NOT call an action. Most "hygiene" rules (intent, redirect, encType) apply only to POST forms.
• Multiple useFetcher() instances on one page — each call returns an independent submission channel; intentional for parallel mutations to different rows.
• useSubmit() in an event handler — correct programmatic submission for autosave, keyboard shortcuts, or onChange triggers.
• Reading fetcher.formData during a submission — intended; this is the canonical optimistic source.
• useActionData data persisting after submission — known behavior; it returns the last action result until the next navigation or action.
• navigate={false} on <Form> — turns it into a fetcher form; equivalent to <fetcher.Form> without holding a fetcher ref.
• unstable_ prefix on parseMultipartFormData / upload handlers — permanent in v2; do not flag as "unstable API".

Context-Sensitive Rules#

Only flag these when the listed condition holds:

IssueFlag ONLY IFNative <form> instead of <Form>Method is POST and the route has an action — GET forms and external-URL forms are fineMissing pending stateThe form is POST and there is no useNavigation() / fetcher.state read anywhere in the componentAction returns json({ ok: true }) after a createThe route is a "/new" or creation surface — same-page edit forms legitimately return JSONmethod="put" / "patch" / "delete"Progressive enhancement is in scope for the surface (public app) — admin/JS-only tools may opt out if documentedUnbounded unstable_createMemoryUploadHandlerThe upload accepts user-controlled files (not a fixed-size internal artifact)Separate routes per mutationThe mutations operate on the same resource with compatible auth — sibling resources with different rules are fineuseNavigation() without formAction filterThe component contains other navigation surfaces (sidebar <Link>, sibling forms) that would trigger false positivesMirroring fetcher.formData into stateThe shadowed value drives a user-visible element (button label, count, toggle) — a local "is-editing" flag is unrelated

Hard gates (before writing findings)#

Run these in order. Do not draft user-facing findings until every gate passes for the batch you are about to report.

1. Location evidence — Pass: Each issue lists a repo path and either a line range or a short verbatim quote from the file you read (not from memory or diff-only guesswork). Name the route module, the component, and the action if one exists.

2. Exemption check — Pass: For each issue, you can state in one line why it is not covered by Valid Patterns (Do NOT Flag) and any matching row in Context-Sensitive Rules.

3. Form-method check — Pass: Before flagging missing intent, missing encType, missing redirect, or missing pending state, you have confirmed the form is method="post" (or put|patch|delete). GET forms are legitimate for search/filter and trigger loaders, not actions — applying POST-form rules to them is a false positive.

4. Protocol — Pass: You completed the Pre-Report Verification Checklist in review-verification-protocol for this review.

Additional Documentation#

• Form vs fetcher misuse — manual fetch(), native <form>, wrong primitive: references/form-vs-fetcher.md
• Pending state anti-patterns — useState flags, page-global vs per-row, missing entirely: references/pending-state.md
• Uploads & FormData validation — unbounded handlers, missing encType, unvalidated keys, mirrored optimistic state: references/uploads-validation.md
• Multi-action routes — intent-pattern violations, PUT/DELETE without PE fallback, missing submit button: references/multi-action-routes.md
• Canonical patterns — see sibling remix-v2-forms

When to Load References#

• Reviewing forms that call fetch() / axios / native <form>, or choose between <Form> and useFetcher → form-vs-fetcher.md
• Reviewing loading flags, spinners, disabled-button logic, per-row pending → pending-state.md
• Reviewing file uploads, unstable_* handlers, FormData parsing, optimistic UI → uploads-validation.md
• Reviewing routes with multiple mutations, intent fields, PUT/DELETE methods → multi-action-routes.md

Review Questions#

1. Does every in-app mutation flow through a route action (no manual fetch())?
2. Is the <Form> vs useFetcher choice driven by whether the URL should change?
3. Is pending state derived from useNavigation() / fetcher.state (never useState)?
4. Are per-row spinners wired to per-row fetcher.state (not page-global useNavigation)?
5. Do file-upload forms set encType="multipart/form-data" and use bounded handlers?
6. Are FormData values validated before reaching the DB?
7. Do multiple mutations on one resource use the intent pattern, not separate routes?
8. Do POST forms have at least one real submit button for progressive enhancement?

False-Positive Notes#

• A <Form> rendering inside a non-route component is still tied to the nearest route's action — read the route file before flagging "missing action".
• useActionData() returning data after a successful submission is expected behavior; the data persists until the next navigation. Only flag if a success banner is rendered unconditionally without a dismiss path.
• Code that imports Form aliased (e.g. import { Form as RemixForm }) is still the Remix component — match on import source, not local name.

Before Submitting Findings#

Complete Hard gates (especially gate 4), then report only issues that still pass the review-verification-protocol pre-report checks.