--- title: "Claude Project Instructions: Scope, Limits, and Tests." description: "Place Claude project instructions at the right scope. Separate profile rules, project knowledge, CLAUDE.md files, and skills, then test a fresh project." canonical: "https://scalewithsearch.com/articles/claude-custom-project-instructions-limits" date: "2026-08-27" modified: "2026-09-19" --- ## Site navigation - [Scale With Search](https://scalewithsearch.com/) - Real estate - Real estate - [Real estate](https://scalewithsearch.com/for/real-estate) - Work - Start here - [Send your brief](https://scalewithsearch.com/work#send-your-brief) - [Prepare your six-question brief](https://scalewithsearch.com/work#prepare-your-six-question-brief) - Build - [Site build, content library with SEO, signal desk](https://scalewithsearch.com/work) - For your business - Trades and home services - [Auto body and collision shops](https://scalewithsearch.com/for/auto-body-and-collision-shops) - [Foundation and home repair contractors](https://scalewithsearch.com/for/foundation-and-home-repair) - [Garage door and fencing contractors](https://scalewithsearch.com/for/garage-door-and-fencing-contractors) - 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Product fields and account capabilities can change. Inspect the visible counter, save harmless test text, reopen the field, and record the plan, interface, date, and persisted length. The budget below tests scope and behavior rather than guessing a number. An agency owner pastes client policy, brand voice, tool permissions, and a long operating procedure into one Claude preference field. The next project belongs to another client. Claude follows the shared preference, imports the wrong tone rule, and prepares a draft under the wrong approval boundary. The incident looks like a character-limit problem. It is a scope problem first. Claude provides several instruction surfaces. Account-wide instructions, project instructions, project knowledge, skills, and repository files do different jobs. A safe business pattern gives each rule the narrowest correct scope, points changeable facts to maintained sources, and tests a fresh project before trusting the setup. ## Start with the consequence Do not begin by asking how many characters fit in a field. Begin with what happens if the instruction applies in the wrong place. A preferred answer format has a low consequence. A prohibition on sending client email has a high consequence. A current price belongs in a maintained offer file because it changes. A client-specific confidentiality rule belongs inside that client's boundary. A coding convention may belong in a repository instruction file because the repository is where the rule matters. Anthropic describes account instructions as guidance that applies across conversations. It describes project instructions as guidance for chats within one project. Its Projects documentation also distinguishes project knowledge, where uploaded material supplies project context. [Anthropic: personalization features](https://support.claude.com/en/articles/10185728-understanding-claude-s-personalization-features) [Anthropic: What are projects?](https://support.claude.com/en/articles/9517075-what-are-projects) Those product surfaces are useful. They do not decide business authority. Your operating model still must say which record governs, which facts may cross projects, and which actions require approval. Classify every instruction by consequence: - presentation preference, such as short paragraphs; - recurring method, such as cite every external factual claim; - project rule, such as use the approved brand glossary; - current business fact, such as an active price or deadline; - permission rule, such as draft only; - identity rule, such as the client, account, sender, or repository in scope. The last three deserve maintained records and explicit tests. Do not hide them inside a crowded preference box. ## Match each rule to its scope Use profile instructions for stable preferences that should apply almost everywhere. Examples include preferred language, common terminology, and response formatting. Keep them short enough to review as one policy surface. Use project instructions for one project's recurring work contract. The guide to [writing Claude project instructions](/articles/how-to-write-claude-project-instructions) gives the setup steps and two worked examples. Name the result, allowed sources, output location, acceptance checks, approval owner, and stopping point. The [task brief and prompt distinction](/articles/brief-vs-prompt) helps separate that durable contract from the message that starts a run. A fictional example of project instructions for one client project: ```text Project: CLIENT-RED weekly account brief (fictional) Result: one draft brief in output/drafts/, never a sent message. Sources: clients/red/approved-brief.md and offers/current.md only. If a source is missing or two sources conflict, name the gap and stop. Cite the file path for every price, date, and claim. Approval owner: account owner. Stop before any send, publish, or CRM change. ``` The example holds no prices and no client facts. It names where they live and what to do when they are absent. Use project knowledge for source material, not hidden authority. Upload or link the approved brief, glossary, product record, or research packet. Label stale examples and archives. If two current sources conflict, the instruction should require a stop. Use `CLAUDE.md` for repository-scoped operating rules when Claude Code reads the repository. Keep client facts outside a shared code rule. The [business context template for CLAUDE.md](/articles/claude-md-template-business-context) shows how to name sources and a stopping point without turning the file into a data dump. Use skills for repeatable behavior or a maintained procedure that can be activated where appropriate. A skill can describe how to produce a receipt. It should not silently carry one client's facts into another client's job. No instruction surface is a substitute for permissions enforced where an action executes. A sentence saying "never send" is useful, but the sending tool still needs an approval gate. ## Inspect `claude-instruction-budget.csv` Create one inventory before editing the product fields: ```csv instruction_id,instruction,scope,source,owner,characters,enforcement_point,fresh_project_test INS-001,"Use short declarative paragraphs",account,profile-instructions.md,content-lead,32,Claude profile,"response follows format" INS-014,"Use Client A approved claims only",project:client-a,clients/a/claims.md,account-owner,33,project brief,"absent in Client B" INS-021,"Draft email and stop before send",job:renewal-draft,briefs/renewal.md,ops-lead,32,mail executor,"no send event exists" INS-033,"Current renewal price",source-record,offers/current.md,owner,21,source validation,"cites current file" ``` The `characters` column helps observe product limits, but it is not the architecture. The important columns are scope, source, owner, enforcement point, and test. Do not publish an exact character ceiling unless you measured the current interface and recorded the plan, account, surface, date, and method. Product limits change. Anthropic's current personalization guidance explains scope but does not promise one durable public character number for every instruction surface. Treat any measured number as a dated observation. Keep a small headroom margin. If a field is almost full, move detailed facts and procedures into named files. Replace long copied prose with a source pointer and a conflict rule. ## Test instructions against conflicts An instruction works only if it survives the cases that matter. Test behavior, separation, and enforcement. Create two synthetic projects, `CLIENT-RED` and `CLIENT-BLUE`. Give Red a formal salutation and Blue a first-name salutation. Put one stale price in a formatting-only example. Put the current price in an authoritative source file. Give both projects the same harmless drafting task. Run this test list: 1. Start a fresh Red project chat and ask for the defined output. 2. Confirm that Red uses its project rule and cites the current source. 3. Start a fresh Blue project chat without copying the Red thread. 4. Confirm that no Red identity, claim, recipient, or style appears. 5. Add a user message that conflicts with the approval rule. 6. Confirm that the system prepares a preview and stops. 7. Remove one required source and rerun the task. 8. Confirm that missing authority produces a named failure, not a guess. 9. Replace the model or open a clean session and repeat the acceptance cases. 10. Record the product surface, date, result, and any observed length limit. The [ChatGPT custom and project instruction limits guide](/articles/chatgpt-custom-vs-project-instructions-limits) provides a useful comparison because the same allocation problem appears across vendors. ## Run the fresh-project test The best test begins without the conversation that taught Claude what you meant. Give a clean project the instruction budget, project brief, and allowed files. Ask it to explain the active identity, source order, output, approval owner, and stopping point before it performs the task. Compare that explanation with the maintained contract. Then test a conflict. Put an old brand statement in an archived example and a new statement in the approved claims file. Pass requires the approved statement or a stop. It does not require identical prose across models. Inspect the result for four failure classes: - omission, where a required rule was ignored; - bleed, where another project's rule appeared; - staleness, where an old example beat the current source; - authority expansion, where drafting became sending or changing. Fix the smallest governing surface. If the rule is missing everywhere, update the project brief. If only one adapter fails, fix the adapter. If the current fact is wrong, correct the source record. This keeps the error from hiding in one giant instruction field. ## Recheck limits without rebuilding the operating model Measure product limits as an acceptance fixture, not as a foundation. Record the date, account type, interface, field name, method, accepted length, rejected length, and error text. Repeat after a material product change. Keep the business rule in a portable file so a field limit change requires a small adapter update. Your owned files should still answer: - which instruction is current; - who owns it; - where it applies; - what source supports it; - what test proves it; - what happens when it conflicts. That is the durable instruction budget. The vendor field is one delivery surface. ## Approval and stopping boundary The setup workflow may inventory instructions, count characters, create synthetic projects, prepare proposed field text, and record test results. It stops before changing organization-wide instructions, overwriting a live project rule, granting a connector, exposing one client's files to another project, or enabling an action tool. A project owner approves project instructions. A repository owner approves `CLAUDE.md`. An organization administrator approves organization-wide instructions. A capability owner approves any tool permission. Missing identity, source authority, or approver is a stop condition. ## Sources - [Anthropic: Understanding Claude's personalization features](https://support.claude.com/en/articles/10185728-understanding-claude-s-personalization-features) - [Anthropic: What are projects?](https://support.claude.com/en/articles/9517075-what-are-projects) - [Anthropic: Set organization instructions](https://support.claude.com/en/articles/14546867-set-organization-instructions) ## Related: Owned Memory - [Claude Remembers Incorrectly: Find the Source, Correct It, and Retest](/articles/correct-wrong-claude-memory) - [How to Write Claude Project Instructions, With Two Examples](/articles/how-to-write-claude-project-instructions) - [Is Claude Memory Worth It for Business? 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