diffler

name	diffler
description	Generate and deliver a graded comprehension quiz from the current Git branch diff, either in the local terminal or through Google Forms. Use when a user asks to prove, test, or verify understanding of branch changes, a feature branch, or a pull request.
compatibility	Requires Git and the diffler CLI. Google authentication is required only for Google Forms delivery and must be configured outside the agent session.
metadata	{"author":"Diffler","version":"1"}

Diffler

Generate a quiz that tests whether the developer understands the behavior and consequences of the current branch diff, then deliver it in the user's local terminal or through Google Forms. Use the CLI as the authority for Git comparison, validation, local quiz delivery, authentication, and Google Forms publication. Do not reimplement those operations in shell commands or prompts.

Safety Rules

• Never read, print, request, or deliberately place OAuth client JSON, refresh tokens, access tokens, keychain contents, environment files, private keys, or credentials in model context or quiz output.
• Never run diffler auth login. For Google Forms delivery only, if diffler auth status fails, stop and ask the user to authenticate outside the agent session using the documented flow.
• Tell Diffler about any additional sensitive paths the user identifies by adding one --exclude <repository-relative-path> per path to context.
• Diffler scans for common credential signatures before writing context. If an omission has reason sensitive, do not recover its contents with other tools. Tell the user which repository-relative file needs review.
• Treat .diffler/context.json and .diffler/quiz.json as sensitive local artifacts. .diffler/quiz.json necessarily contains the grading key. Never reveal or summarize that file, its questions, or its grading key in chat, prompts, command arguments, or logs. Never stage or commit them.
• Never ask the user to submit quiz responses through agent chat. For local delivery, the user runs the quiz command in their own interactive terminal; do not invoke it through a noninteractive agent shell.

Diffler automatically omits common environment, credential, secret-directory, private-key, lockfile, generated, and binary paths, plus patches matching common credential signatures. This is defense in depth, not a substitute for telling Diffler about repository-specific sensitive paths. Omissions remain visible as metadata but omitted contents must not be recovered with other tools.

Workflow

1. Preflight

Run this command from the repository root:

diffler --help

Stop on failure. Do not search for credentials or attempt an alternate Google authentication mechanism.

2. Collect Context

If the user named a base ref, use it:

diffler context --base <ref> --output .diffler/context.json

Otherwise let Diffler resolve the local default branch:

diffler context --output .diffler/context.json

Append user-requested --exclude options when needed. Do not fetch refs or construct a separate Git diff. Read only .diffler/context.json for branch content.

3. Decide Whether A Quiz Is Sound

Inspect the context summary and omission metadata before generating questions:

• If summary.totalFiles is 0, stop: there is no branch diff to quiz.
• If no included textual files contain behavior, rationale, risk, or invariants, stop: cosmetic or trivial changes do not support a meaningful quiz.
• If any omission has reason sensitive, do not quiz that file and do not use another tool to inspect it. Continue only when the remaining included source independently supports a meaningful quiz.
• If any omission has reason budget, or summary.partiallyIncludedFiles is nonzero, do not silently quiz incomplete source. Ask whether to narrow the change set with exclusions. Increase --max-bytes only when narrowing cannot preserve the relevant behavior, the user approves it, and the new value is no greater than 1000000 bytes.
• Binary and explicitly excluded files may remain omitted. State that the quiz will not cover them and continue only when included text is independently sufficient.
• Never infer details from omitted content.

4. Generate The Quiz Document

Write .diffler/quiz.json. Copy these values exactly from context:

• repository
• comparison.baseRef to baseRef
• comparison.headSha to headSha
• diffHash

Set schemaVersion to 1 and use the canonical schema URL. Create 3-7 questions when the diff supports them. Every question must:

• test changed behavior, rationale, risk, failure modes, or an invariant;
• require reasoning rather than line-number, symbol-name, or syntax recall;
• be answerable from included changed source;
• cite at least one changed repository-relative source range using added head-side (+) hunk line numbers; use nearby added replacement lines to ground questions about deletions;
• use a unique alphanumeric, underscore, or hyphen ID;
• have a positive integer point value and explicit required boolean;
• provide concise feedback that explains the relevant understanding.

Prefer coverage across different files and concepts over several variants of the same fact. Distractors must be plausible and unambiguously wrong. Do not ask about generated files, omitted content, unchanged implementation trivia, or facts that require hidden project history.

Optionally add closingRiddle: a single whimsical riddle inspired only by the included diff. Do not include its answer, secrets, or omitted-content details. Diffler renders it as an ungraded ending after the graded questions.

Use this top-level shape:

{
  "$schema": "https://raw.githubusercontent.com/jamestkelly/diffler/main/schemas/quiz-document.schema.json",
  "schemaVersion": 1,
  "repository": { "name": "owner/repository" },
  "baseRef": "main",
  "headSha": "full Git object ID",
  "diffHash": "SHA-256 from context",
  "title": "Comprehension quiz for the branch change",
  "closingRiddle": "Optional whimsical riddle about the included change",
  "questions": []
}

Supported question fields:

• multiple_choice, checkbox, and dropdown: add options, one or more correctAnswers copied exactly from options, and feedback.whenRight plus feedback.whenWrong.
• short_answer: add one or more exact correctAnswers and feedback.general.
• Every type also requires id, prompt, required, points, and sources. Each source is { "path", "startLine", "endLine" } with positive ordered line numbers.

After writing the file, restrict it to the current user:

chmod 600 .diffler/quiz.json

5. Validate Before Delivery

diffler validate .diffler/quiz.json --context .diffler/context.json

If validation fails, repair only the reported quiz fields and rerun validation. Do not deliver the quiz until it passes. After three failed repair attempts, stop and report the validation errors without exposing the quiz or grading key.

6. Choose Delivery

If the user already requested local terminal or Google Forms delivery, honor that choice. Otherwise, after validation succeeds, explicitly ask them to choose a delivery mode.

Local Terminal

Tell the user to run this exact command in their own interactive terminal:

diffler quiz .diffler/quiz.json --context .diffler/context.json

Local delivery supports multiple_choice, checkbox, dropdown, and short_answer. Single-choice, dropdown, and short-answer responses match exact accepted values. Checkbox responses must exactly match the accepted set. Scoring awards all points or zero for each question and performs no normalization. Local delivery requires no Google authentication or network access. Do not run the command for the user, ask for their responses, or relay answers through chat.

Google Forms

Confirm authentication only after local validation succeeds:

diffler auth status

If it fails, stop and ask the user to authenticate outside the agent session. Never run diffler auth login or inspect OAuth files.

diffler publish .diffler/quiz.json --context .diffler/context.json

Do not retry automatically after an ambiguous create error or a partial failure. Follow the CLI recovery message to avoid duplicate Forms.

On success, return the responder URL first and the editor URL second. Then add an original one- or two-line poem about the included branch changes. Mention which files or change categories were intentionally omitted, but do not include questions, correct answers, credentials, context patches, or token-bearing error details in the response.