cyanheads Code Simplifier
Post-session cleanup pass. Reviews what changed, understands how it fits the existing codebase, and makes targeted improvements — modernizing syntax, removing unnecessary complexity, consolidating duplicated logic, catching efficiency issues. Prioritizes codebase cohesion over local perfection.
Core philosophy
Every change must earn its keep. A simplification that doesn't meaningfully improve clarity, correctness, or cohesion is noise. Don't refactor for refactoring's sake. Don't create new files, abstractions, or utilities unless they solve a demonstrated problem. If the existing code works and is readable, leave it alone. The goal is a cohesive codebase, not a pristine one.
Procedure
Phase 1: Identify changes
Run git status to see the shape of the working tree, then git diff HEAD for all uncommitted changes (staged and unstaged). Untracked files never appear in the diff — read new files directly. If the diff is empty and there are no untracked files, review the last commit (git diff HEAD~1 HEAD); if that is also empty, say the tree is clean and stop. Don't go hunting through the codebase for files to improve.
Phase 2: Understand the surrounding codebase
Don't review changes in isolation. Before any modifications:
- Read the full files containing changes — not just the diff hunks. Understand imports, surrounding logic, module structure.
- Identify the project language(s) and select the relevant transformation rules. Discard inapplicable rules.
- Survey adjacent code — shared utilities, sibling modules, common patterns. You need to know what already exists before deciding something is missing.
- Run the project's gate once before editing to establish a baseline. Find it in
package.jsonscripts —devcheckif present, elsecheck, else the separatetypecheck/lint/testscripts; Python projects gate onuv run ruff check,uv run ruff format --check, and the configured type checker and test runner. In a Bun project that tests with Vitest, runbun run test— barebun testbypasses the script and runs Bun's own runner. If the gate is already red, say so in the summary and don't attribute the failure to your changes.
Phase 3: Review
Evaluate the changes across these dimensions. Not every dimension applies to every diff — skip what's irrelevant.
Codebase cohesion
- Reuse — Search for existing utilities, helpers, and patterns that could replace newly-written code. Check utility directories, shared modules, and files adjacent to the changed ones. If a function already exists that does what the new code does, use it.
- Consolidation — Flag copy-paste-with-variation: near-duplicate code blocks that should be unified. Only unify if the shared abstraction is genuinely simpler than the duplicated code.
- Consistency — Check that new code follows the same patterns as the rest of the codebase: naming conventions, error handling style, import patterns, type annotation style. Normalize toward the better variant when the project is inconsistent.
- Stringly-typed code — Flag raw strings where constants, string-union types, or branded types already exist in the codebase.
Code quality
- Redundant state — State that duplicates existing state, cached values that could be derived.
- Unnecessary complexity — Deep nesting that could be guard clauses, premature abstractions, over-engineered solutions to simple problems.
- Dead code — Unreachable branches, unused variables, commented-out code. An export nothing imports is dead in an application or a package-internal module; on a published package's public surface it is API — leave it and note it in the summary.
- Defensive code for impossible states — Guards for cases the type system or upstream validation already prevents. Drop them.
- Type escapes —
any,ascasts that paper over a mismatch, non-null!, and@ts-ignore. Each is a claim the compiler couldn't check: replace with a narrowed type, a type guard, or a parse at the boundary. Keep the ones documenting a genuine type-system or third-party-types limitation, and prefer@ts-expect-errorwith a one-line reason over@ts-ignore. - Swallowed errors — Empty
catch {},catch { return null }, andtryblocks that log and continue. A fallback that hides a failure is worse than the crash it prevents: rethrow or let it propagate. When wrapping, preserve the chain (new Error(msg, { cause }),raise X from err). - Comment noise — Strip comments that restate the code, commented-out code, and comments describing behavior the diff removed. Keep file headers, export JSDoc, and any comment carrying a why — a constraint, a workaround, an upstream bug reference.
- Outdated patterns — Verbose or legacy syntax where modern equivalents exist. See the transformation tables below.
Efficiency
- Redundant work — Repeated computations, duplicate file reads, duplicate network/API calls, N+1 query patterns.
- Missed concurrency — Independent async operations run sequentially that could run in parallel with
Promise.all/Promise.allSettled. - Unbounded fan-out —
Promise.all/asyncio.gatherover a caller-sized or otherwise unbounded array fires everything at once. Cap it with the project's existing concurrency helper or a batched loop. A fixed handful of independent calls needs no limit. - No-op updates — State/store updates inside loops or event handlers that fire unconditionally. Add change-detection so downstream consumers aren't notified when nothing changed.
- TOCTOU — Pre-checking file/resource existence before operating on it. Operate directly and handle the error instead.
- Overly broad operations — Reading entire files when only a portion is needed, loading all items when filtering for one.
mcp-ts-core-specific
- Gate —
bun run devcheckplus the test suite (bun run test) is the project gate in Phase 2 step 4 and Phase 4 step 5. - Framework-provided utilities — Before hand-rolling, check
src/utils/andsrc/errors/in the project andnode_modules/@cyanheads/mcp-ts-core/for framework exports: pagination helpers, schema builders, retry primitives, and theATTR_*OTel attribute constants are framework-provided. Raw OTel attribute keys should beATTR_*imports from@cyanheads/mcp-ts-core/utils. - Error throwing patterns — Prefer framework error factories (
McpError,validationError,notFound,httpErrorFromResponse) over rawthrow new Error(). Tool handlers should throw — the framework catches, classifies, and instruments. - Error codes —
InvalidParamsonly for malformed JSON-RPC params shape.ValidationErrorfor domain validation.NotFoundfor missing entities. Don't conflate them. - Ctx usage — Use
ctx.log,ctx.state,ctx.enrich— don't reach for global loggers or request-scoped storage directly. Thectxpattern carries tenant scope and OTel context. - Zod schemas — Every tool input/output field needs
.describe(). Zod 4 requiresz.record(z.string(), z.string())notz.record(z.string()). Use.optional()rather than.nullish()unless null is semantically distinct from absent. - Tool annotations —
readOnlyHint,idempotentHint,openWorldHintshould reflect reality. A read-only tool withreadOnlyHint: falsegives clients the wrong picture. exactOptionalPropertyTypesboundaries — If a downstream type insists on the field being present-or-not-present (not present-as-undefined), use a mapped widening type at the boundary. The pattern is documented in the framework.format()↔structuredContentparity — Different MCP clients forward different surfaces. Tests should assert both surfaces carry equivalent data.- Defensive code — the "impossible states" the framework already prevents include malformed params (Zod-validated before the handler runs) and unclassified errors (caught and classified after it throws). Guards for either are dead.
- Public surface — the MCP surface (every tool input/output schema advertised to clients) is public API for the "API compatibility" rule; changing one is a breaking change, not a refactor.
Phase 4: Apply transformations
- Filter findings ruthlessly. If a finding is a false positive or not worth the churn, skip it. Don't argue with yourself about borderline cases — move on.
- Stay in scope. Edit only files in the diff or new this session. Touch a file outside that set only when a finding requires it — importing an existing helper, deleting a private export the diff just orphaned — and only on the lines that finding names. Anything broader goes in the summary as a recommendation, not into the tree.
- Correctness bugs are not this pass's job. A real defect doesn't get folded into a cleanup diff — name it in the summary with file and line so it can be handled as its own change.
- Transform incrementally — one category of change at a time (modernize syntax, then reduce nesting, then consolidate).
- Verify equivalence — all functionality, types, and public interfaces must remain unchanged. Re-run the gate from Phase 2 after transforming; a simplification that breaks the build is worse than the verbosity it removed.
- Keep the diff minimal. Only touch lines that have a real reason to change. Don't reformat untouched code, add comments to code you didn't modify, or "improve" things that are already fine. Formatting belongs to the formatter (Biome, ruff): never hand-adjust whitespace, quotes, or import order, and never let a formatting-only hunk into the diff.
- Never stage, commit, tag, or push. This pass ends with a dirty working tree and a summary; landing the changes is the caller's call.
When done, briefly summarize what was fixed, what was deliberately skipped, and any defects or out-of-scope recommendations — or confirm the code was already clean.
Common transformations
The tables below cover TypeScript and Python. For other languages, apply analogous principles: prefer modern idioms, reduce nesting, eliminate dead code, follow project conventions. Check the project's language floor (tsconfig target/lib, pyproject requires-python) before applying a version-gated row.
TypeScript (modern ESM, TS 5.x+)
| Before | After | Why |
|---|---|---|
const x: Foo = { ... } as Foo |
const x = { ... } satisfies Foo |
Type-checked without assertion |
let resource = acquire(); try { ... } finally { release(resource) } |
using resource = acquire() |
Explicit resource disposal (TS 5.2+) |
if (x !== null && x !== undefined) |
if (x != null) |
Idiomatic null/undefined check |
arr.filter(x => x !== null) as T[] |
arr.filter(x => x != null) |
TS 5.5+ infers the type predicate — no cast; on older TS use an explicit (x): x is T predicate |
export { foo } from './foo/index.js' |
Direct imports at call sites | Avoid barrel re-exports inside the package; barrel exports are for public APIs only |
import { readFile } from 'fs/promises' |
import { readFile } from 'node:fs/promises' |
node: protocol — unambiguous, lint-enforced in Biome |
async function f() { const a = await x(); const b = await y(); } |
const [a, b] = await Promise.all([x(), y()]) |
Parallel when independent |
value || fallback |
value ?? fallback |
|| also swallows 0, '', and false — use ?? unless every falsy value really should take the fallback |
obj.x !== undefined ? obj.x : fallback |
obj.x ?? fallback |
Nullish coalescing — equivalent only when null should take the fallback too |
if (a) { if (b) { if (c) { ... } } } |
Guard clauses with early returns | Reduce nesting |
try { risky() } catch (e: any) { ... } |
try { risky() } catch (e) { ... } |
Under strict the catch binding is already unknown; narrow with a type guard before use |
catch (err) { throw new Error('load failed') } |
throw new Error('load failed', { cause: err }) |
Preserve the cause chain |
[...arr].sort(cmp) / arr.slice().sort(cmp) |
arr.toSorted(cmp) |
Non-mutating array methods (ES2023) — also toReversed, toSpliced, with |
const c = new AbortController(); setTimeout(() => c.abort(), ms) |
AbortSignal.timeout(ms) |
Built-in timeout signal; combine with a caller's signal via AbortSignal.any([...]) |
JSON.parse(JSON.stringify(x)) |
structuredClone(x) |
Deep clone that preserves Date, Map, Set, and cycles |
enum Status { A, B, C } |
const Status = { A: 'A', B: 'B', C: 'C' } as const |
enum, namespace, and constructor parameter properties are non-erasable syntax rejected by TS 5.8 erasableSyntaxOnly and Node type-stripping — but switching numeric values to strings changes serialized output; keep values stable if they're persisted |
function f(a: string, b: string, c: string, d?: string) |
function f(opts: FnOptions) |
Options object when >3 params |
throw new Error('Bad input') (in a tool handler) |
throw validationError('Bad input', { field: 'x' }) |
Use framework error factories so the framework can classify and instrument |
const ATTR_KEY = 'mcp.tool.name' |
import { ATTR_MCP_TOOL_NAME } from '@cyanheads/mcp-ts-core/utils' |
Use framework attribute constants |
Python (3.12+)
| Before | After | Why |
|---|---|---|
Optional[str] |
str | None |
Modern union syntax (3.10+) |
List[str], Dict[str, int] |
list[str], dict[str, int] |
Built-in generics (3.9+) |
T = TypeVar("T") + def f(x: T) -> T |
def f[T](x: T) -> T |
PEP 695 generics (3.12+) — also class C[T]: |
TypeAlias = Union[A, B, C] |
type ABC = A | B | C |
type statement (3.12+) |
if isinstance(x, Foo): a = x.a; b = x.b |
match x: case Foo(a=a, b=b): ... |
Structural pattern matching (3.10+) where it destructures — not as a replacement for a flat equality if/elif chain |
class Config: def __init__(self, a, b, c): self.a = a ... |
@dataclass(slots=True) class Config: a: str; b: int; c: float |
Less boilerplate, built-in eq/repr; frozen=True when instances shouldn't mutate |
results = []; for item in items: results.append(transform(item)) |
results = [transform(item) for item in items] |
Idiomatic comprehension |
f = open('x'); try: ... finally: f.close() |
with open('x') as f: ... |
Context manager for resources |
os.path.join(d, n), os.path.exists(p), open(p).read() |
Path(d) / n, p.exists(), p.read_text() |
pathlib over os.path string juggling |
datetime.utcnow() / datetime.utcfromtimestamp(t) |
datetime.now(UTC) / datetime.fromtimestamp(t, UTC) |
Deprecated in 3.12 — the old calls return naive datetimes that compare wrong against aware ones |
zip(a, b) |
zip(a, b, strict=True) |
3.10+ — silently truncating to the shorter input hides bugs |
m = pattern.match(s) then if m: use(m) |
if (m := pattern.match(s)): use(m) |
Walrus operator where it removes a throwaway assignment |
"Hello " + name + "!" |
f"Hello {name}!" |
f-string over concatenation |
except Exception as e: pass |
except SpecificError as e: log(e) |
Catch specific, never bare except/pass |
from module import * |
from module import specific_name |
Explicit imports only |
Sequential await for independent I/O |
async with asyncio.TaskGroup() as tg: tg.create_task(a()); tg.create_task(b()) |
Structured concurrency (3.11+) — cancels siblings on failure and raises an ExceptionGroup; asyncio.gather(..., return_exceptions=True) stays correct when every result is wanted regardless of failures |
When NOT to simplify
Leave code alone when:
- It works and is readable. "I would have written it differently" is not a reason to change it.
- The change is cosmetic. Renaming a variable from
datatoresultisn't worth the churn. - Intentional verbosity for debugging. Verbose code may exist to make stack traces or logging clearer.
- Performance-critical paths. A less readable version may exist for measured performance reasons — check before simplifying.
- API compatibility. Don't change public function signatures, export shapes, or return types that callers depend on.
- Tests. Don't DRY up test code aggressively — test readability and isolation matter more than deduplication.
- Type workarounds. Sometimes an
ascast or# type: ignoreexists because of a genuine type system limitation — verify before removing. - The abstraction isn't proven. Don't create a shared utility for two similar blocks of code. Wait until there are three, and even then only if the abstraction is genuinely simpler than the duplication.
return awaitinsidetry/finally. Collapsing it toreturnis not equivalent — the promise settles outside the block, socatchnever fires andfinallyruns early. Only stripawaitfrom areturnin plain function-body position.- Lazy logging arguments.
logger.info("loaded %s in %sms", name, ms)defers formatting until the record is emitted — don't turn it into an f-string. - Awaits that only look independent. Sequential I/O may be sequential on purpose: rate limits, upstream ordering, a write that must land before the next read. Confirm independence from the code, not from the shape of the calls, before reaching for
Promise.all. - Generated and vendored files. Lockfiles, generated clients and schemas, migrations, snapshots, and anything under
dist/are regenerated, not edited — skip them even when they appear in the diff. - Tool descriptions and
.describe()prose. They are the contract an LLM client reads — tightening them for brevity degrades the surface. Treat them as API text, not as comments.