“I want a small open-source MCP retrieval router that defaults to grep and only falls through to vector search when the query actually looks semantic. Worth shipping?”
GrepFirst McFallthrough
“Finally, someone who remembers that grep is O(n) and your RAM isn't free.”
An MCP-native retrieval router that classifies incoming queries as lexical vs. semantic and dispatches to ripgrep or a vector store accordingly, with zero config defaults.
The MCP tooling layer is genuinely underbuilt right now and retrieval routing is a real unsolved DX problem. grep-first is the correct default that almost nobody implements — everyone cargo-cults vector search. This is small enough to ship fast and specific enough to find an audience in the Claude/Cursor power-user community immediately.
Viability Analysis
Pros & Cons
What's going for it
What's against it
Who You're Up Against
Open Source Alternatives
When Will Big AI Kill This?
Most Likely Killer
Anthropic
Timeline: 9-18 months
How They'll Do It
They add a retrieval_strategy hint to the MCP spec or ship a reference retrieval server with hybrid routing baked in, making your router redundant by default
Your Survival Strategy
Own the classification logic as a reusable library that works regardless of transport — make GrepFirst the algorithm, not just the MCP server
Confidence
If You're Crazy Enough to Build It
Solo Dev Time
1 focused weekend for v0.1, 3 weeks to handle edge cases you'll regret ignoring
Team Size
One developer who has strong opinions about BM25 and isn't afraid to read ripgrep source code
Estimated Cost
$0 in infra if local, ~$20/month if you add a hosted demo with embeddings API calls
Tech Stack
How this was generated
Production-readiness odds
Real readiness gaps. Build a thin first, harden second; budget runway for both.
ANCHORED TO OUR OWN READINESS RUBRIC — NO EXTERNAL STAT CITED
🛡 Safety considerations
What these mean →Heuristic, not exhaustive. Surfaces the 3 biggest categories an operator should think about for this idea. Hover any chip for the mitigation pointer.
⚖ Governance checklist
7 controls applyThings to have in place before you ship. Pairs with the OWASP-style risk chips above — that catalog answers “what could go wrong?”, this one answers “what should you have ready?”
Audit trail of every tool call
criticalPersist a structured per-call log of inputs, outputs, and decisions for at least the legal retention window. Without this, post-incident review is impossible.
Role-based access control on the agent surface
criticalDifferent users, different scopes. The agent should never default to "admin can do everything." Pair with per-task capability scoping.
Tenant / workspace isolation
criticalA multi-tenant agent must never leak data across tenants in either direction (inputs OR cached intermediate state).
Secrets management
highTokens and API keys live in a vault, not in env vars on a CI runner. Rotate on a documented schedule, not "when something happens."
Eval coverage on every release
highA frozen eval suite that runs on every model / prompt change. "It worked when I demoed it" is not a release gate.
Per-user / per-tenant rate limits
mediumAgent loops are pathologically expensive when wrong. Cap tokens-per-session, tool-calls-per-session, and dollars-per-day before launch.
Pin model versions; track the changelog
mediumA silent provider-side model upgrade can shift behavior overnight. Pin to a versioned model ID; subscribe to the provider changelog.
OUR INTERNAL TWELVE-CONTROL SYNTHESIS — STANDARD SOC 2 / ISO 27001 / GDPR FAMILIES APPLIED TO LLM AGENTS
Agent-Readiness Score
Worth building, but plan for the long-tail. GrepFirst McFallthrough needs runway, not just speed.
- Memory ↗21/25
Some cross-session state — start with Redis, graduate to a vector store.
- Tools ↗9/25
Crowded market: at least 8 integrations to compete.
- Policy ↗11/25
Mid-size policy surface — define refusal categories before launch.
- Evals ↗17/25
Eval scaffolding doable — write 50 paired examples and grade with an LLM-as-judge.
DETERMINISTIC SCORE — DERIVED FROM EXISTING ANALYSIS, NO SECOND LLM CALL
🛠 Build this with Claude Code
Skip the boilerplate. Start from a working spec.
We've packaged this idea into a CLAUDE.md + scaffold.sh starter — the problem statement, agent-readiness sub-scores, suggested tools, and smoke evals, all deterministic and ready to drop into a fresh repo. Open it in Claude Code, or copy the markdown into any IDE.
Don't have Claude Code yet? View the bootstrap preview · grab the JSON bundle · or embed the readiness badge.
🛠 Steal this idea
Going to build GrepFirst McFallthrough? Claim it.
Post a public 2-paragraph plan. Add the repo URL when you ship. No rights granted; no permission required — credit goes to whoever ships first. See all claims at /steal-this-idea.
Want to actually build this?
Work with me to ship it.
Survived the verdict? Good. Let's build the damn thing.
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